Asbestos-Induced Mesothelial to Fibroblastic Transition Is Modulated by the Inflammasome

The in vitro cytotoxic effects of natural (fibrous epsomite crystals) and synthetic (Epsom salt) magnesium sulfate

Exposure to mineral fibers represents an occupational and environmental hazard since particulate inhalation leads to several health disorders. However, few data are available on the effect of fibers with high solubility like natural epsomite, a water-soluble fiber with an inhalable size that allows it to penetrate biological systems, with regard to the respiratory tract. This study evaluated the natural (fibrous epsomite) and synthetic (Epsom salt) magnesium sulfate pathogenicity. Investigations have been performed through morpho-functional and biochemical analyses, in an in vitro cell model that usually grows as monocytes, but that under appropriate conditions differentiates into macrophages. These latter, known as alveolar macrophages, if referred to lungs, represent the first line of defense against harmful inhaled stimuli. Morphological observations reveal that, if Epsom salt induces osmotic stress on cell culture, natural epsomite fibers lead to cellular alterations including thickening of the nuclear envelope and degenerated mitochondria. Moreover, the insoluble fraction (impurities) internalized by cells induces diffuse damage characterized at the highest dosage and exposure time by secondary necrosis or necrotic cell death features. Biochemical analyses confirm this mineral behavior that involves MAPK pathway activation, resulting in many different cellular responses ranging from proliferation control to cell death. Epsom salt leads to MAPK/ERK activation, a marker predictive of overall survival. Unlike, natural epsomite induces upregulation of MAPK/p38 protein involved in the phosphorylation of downstream targets driving necrotic cell death. These findings demonstrate natural epsomite toxicity on U937 cell culture, making the inhalation of these fibers potentially hazardous for human health. RESEARCH HIGHLIGHTS: Natural epsomite and synthetic Epsom salt effects have been evaluated in U937 cell model. Epsom salt induces an osmotic cellular stress. Natural epsomite fibers lead to cellular damage and can be considered potentially dangerous for human health.

Food-derived peptides as novel therapeutic strategies for NLRP3 inflammasome-related diseases: a systematic review

NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3), a member of the nucleotide-binding domain (NOD) and leucine-rich repeat sequence (LRR) protein (NLR) family, plays an essential role in the inflammation initiation and inflammatory mediator secretion, and thus is also associated with many disease progressions. Food-derived bioactive peptides (FDBP) exhibit excellent anti-inflammatory activity in both in vivo and in vitro models. They are encrypted in plant, meat, and milk proteins and can be released under enzymatic hydrolysis or fermentation conditions, thereby hindering the progression of hyperuricemia, inflammatory bowel disease, chronic liver disease, neurological disorders, lung injury and periodontitis by inactivating the NLRP3. However, there is a lack of systematic review around FDBP, NLRP3, and NLRP3-related diseases. Therefore, this review summarized FDBP that exert inhibiting effects on NLRP3 inflammasome from different protein sources and detailed their preparation and purification methods. Additionally, this paper also compiled the possible inhibitory mechanisms of FDBP on NLRP3 inflammasomes and its regulatory role in NLRP3 inflammasome-related diseases. Finally, the progress of cutting-edge technologies, including nanoparticle, computer-aided screening strategy and recombinant DNA technology, in the acquisition or encapsulation of NLRP3 inhibitory FDBP was discussed. This review provides a scientific basis for understanding the anti-inflammatory mechanism of FDBP through the regulation of the NLRP3 inflammasome and also provides guidance for the development of therapeutic adjuvants or functional foods enriched with these FDBP.

Molecular and Cellular Mechanism of Action of Chrysotile Asbestos in MRC5 Cell Line

Asbestos is a known carcinogen; however, the influence of chrysotile asbestos on the development of tumor-related diseases remains a subject of intense debate within the scientific community. To analyze the effect of asbestos, we conducted a study using the MRC5 cell line. We were able to demonstrate that chrysotile asbestos stimulated the production of reactive oxygen species (ROS), leading to cell death and DNA damage in the MRC5 cell line, using various techniques such as ROS measurement, comet assay, MTT assay, and qPCR. In addition, we found that chrysotile asbestos treatment significantly increased extracellular mitochondrial DNA levels in the culture medium and induced significant changes in the expression profile of several miRNAs, which was the first of its kind. Thus, our research highlights the importance of studying the effects of chrysotile asbestos on human health and reveals multiple adverse effects of chrysotile asbestos.

Perfluoroalkyl Substances (PFAS) Affect Inflammation in Lung Cells and Tissues

Adverse lung outcomes from exposure to per-and polyfluoroalkyl substances (PFAS) are known; however, the mechanism of action is poorly understood. To explore this, human bronchial epithelial cells were grown and exposed to varied concentrations of short-chain (perfluorobutanoic acid, perflurobutane sulfonic acid and GenX) or long-chain (PFOA and perfluorooctane sulfonic acid (PFOS)) PFAS, alone or in a mixture to identify cytotoxic concentrations. Non-cytotoxic concentrations of PFAS from this experiment were selected to assess NLRP3 inflammasome activation and priming. We found that PFOA and PFOS alone or in a mixture primed and activated the inflammasome compared with vehicle control. Atomic force microscopy showed that PFOA but not PFOS significantly altered the membrane properties of cells. RNA sequencing was performed on the lungs of mice that had consumed PFOA in drinking water for 14 weeks. Wild type (WT), PPARα knock-out (KO) and humanized PPARα (KI) were exposed to PFOA. We found that multiple inflammation- and immune-related genes were affected. Taken together, our study demonstrated that PFAS exposure could alter lung biology in a significant manner and may contribute to asthma/airway hyper-responsiveness.

Variant Enrichment Analysis to Explore Pathways Disruption in a Necropsy Series of Asbestos-Exposed Shipyard Workers

The variant enrichment analysis (VEA), a recently developed bioinformatic workflow, has been shown to be a valuable tool for whole-exome sequencing data analysis, allowing finding differences between the number of genetic variants in a given pathway compared to a reference dataset. In a previous study, using VEA, we identified different pathway signatures associated with the development of pulmonary toxicities in mesothelioma patients treated with radical hemithoracic radiation therapy. Here, we used VEA to discover novel pathways altered in individuals exposed to asbestos who developed or not asbestos-related diseases (lung cancer or mesothelioma). A population-based autopsy study was designed in which asbestos exposure was evaluated and quantitated by investigating objective signs of exposure. We selected patients with similar exposure to asbestos. Formalin-fixed paraffin-embedded (FFPE) tissues were used as a source of DNA and whole-exome sequencing analysis was performed, running VEA to identify potentially disrupted pathways in individuals who developed thoracic cancers induced by asbestos exposure. By using VEA analysis, we confirmed the involvement of pathways considered as the main culprits for asbestos-induced carcinogenesis: oxidative stress and chromosome instability. Furthermore, we identified protective genetic assets preserving genome stability and susceptibility assets predisposing to a worst outcome.

IL-17A Promotes the Migration, Invasion and the EMT Process of Lung Cancer Accompanied by NLRP3 Activation

Background

Lung cancer is a deadly cancer worldwide, and its pathogenesis and treatment methods require continuous research and exploration. As a representative factor of adaptive immunity, the role of interleukin-17A (IL-17A) in lung cancer is still unclear. The purpose of the present study was to investigate the effect of IL-17A on the biological behaviour of lung cancer cells and the relative mechanism.

Methods

The human lung adenocarcinoma A549 and H1299 cell lines were used for in vitro study. The effects of IL-17A on cell proliferation, migration and invasion were assessed by CCK-8 assay, wound-healing assay, transwell invasion assay and real-time cell analysis (RTCA). The expression levels of marker proteins in the process of epithelial-mesenchymal transition (EMT) were detected by western blot analysis. Caspase-1 activity and the concentration of IL-1β after NLRP3 inflammasome activation were measured by a Caspase-1 Activity Assay Kit and an IL-1β ELISA kit, respectively.

Results

Compared to the control group, IL-17A treatment did not affect the proliferation of A549 and H1299 cells in vitro, but it promoted cell migration, invasion and the EMT process. IL-17A treatment increased NLRP3 expression, caspase-1 activity and IL-1β level. Blockade of NLRP3 alleviated the cell migration, invasion and the EMT process induced by IL-17A.

Conclusions

In conclusion, these findings indicated that NLRP3 participates in the migration, invasion and the EMT process of IL-17A-stimulated lung cells in vitro.

The Acute Toxicity of Mineral Fibres: A Systematic In Vitro Study Using Different THP-1 Macrophage Phenotypes

Alveolar macrophages are the first line of defence against detrimental inhaled stimuli. To date, no comparative data have been obtained on the inflammatory response induced by different carcinogenic mineral fibres in the three main macrophage phenotypes: M0 (non-activated), M1 (pro-inflammatory) and M2 (alternatively activated). To gain new insights into the different toxicity mechanisms of carcinogenic mineral fibres, the acute effects of fibrous erionite, crocidolite and chrysotile in the three phenotypes obtained by THP-1 monocyte differentiation were investigated. The three mineral fibres apparently act by different toxicity mechanisms. Crocidolite seems to exert its toxic effects mostly as a result of its biodurability, ROS and cytokine production and DNA damage. Chrysotile, due to its low biodurability, displays toxic effects related to the release of toxic metals and the production of ROS and cytokines. Other mechanisms are involved in explaining the toxicity of biodurable fibrous erionite, which induces lower ROS and toxic metal release but exhibits a cation-exchange capacity able to alter the intracellular homeostasis of important cations. Concerning the differences among the three macrophage phenotypes, similar behaviour in the production of pro-inflammatory mediators was observed. The M2 phenotype, although known as a cell type recruited to mitigate the inflammatory state, in the case of asbestos fibres and erionite, serves to support the process by supplying pro-inflammatory mediators.

Characterization of Fibrous Wollastonite NYAD G in View of Its Use as Negative Standard for In Vitro Toxicity Tests

Today, despite considerable efforts undertaken by the scientific community, the mechanisms of carcinogenesis of mineral fibres remain poorly understood. A crucial role in disclosing the mechanisms of action of mineral fibres is played by in vitro and in vivo models. Such models require experimental design based on negative and positive controls. Commonly used positive controls are amosite and crocidolite UICC standards, while negative controls have not been identified so far. The extensive characterisation and assessment of toxicity/pathogenicity potential carried out in this work indicate that the commercial fibrous wollastonite NYAD G may be considered as a negative standard control for biological and biomedical tests involving mineral fibres. Preliminary in vitro tests suggest that wollastonite NYAD G is not genotoxic. This material is nearly pure and is characterized by very long (46.6 µm), thick (3.74 µm) and non-biodurable fibres with a low content of metals. According to the fibre potential toxicity index (FPTI) model, wollastonite NYAD G is an inert mineral fibre that is expected to exert a low biological response during in vitro/in vivo testing.

Contribution of Mitochondrial Dysfunction Combined with NLRP3 Inflammasome Activation in Selected Neurodegenerative Diseases

Alzheimer's disease and Parkinson's disease are the most common forms of neurodegenerative illnesses. It has been widely accepted that neuroinflammation is the key pathogenic mechanism in neurodegeneration. Both mitochondrial dysfunction and enhanced NLRP3 (nucleotide-binding oligomerization domain (NOD)-like receptor protein 3) inflammasome complex activity have a crucial role in inducing and sustaining neuroinflammation. In addition, mitochondrial-related inflammatory factors could drive the formation of inflammasome complexes, which are responsible for the activation, maturation, and release of pro-inflammatory cytokines, including interleukin-1β (IL-1β) and interleukin-18 (IL-18). The present review includes a broadened approach to the role of mitochondrial dysfunction resulting in abnormal NLRP3 activation in selected neurodegenerative diseases. Moreover, we also discuss the potential mitochondria-focused treatments that could influence the NLRP3 complex.

NLRP3 Inflammasome: The Stormy Link Between Obesity and COVID-19

Several countries around the world have faced an important obesity challenge for the past four decades as the result of an obesogenic environment. This disease has a multifactorial origin and it is associated with multiple comorbidities including type 2 diabetes, hypertension, osteoarthritis, metabolic syndrome, cancer, and dyslipidemia. With regard to dyslipidemia, hypertriglyceridemia is a well-known activator of the NLRP3 inflammasome, triggering adipokines and cytokines secretion which in addition induce a systemic inflammatory state that provides an adequate scenario for infections, particularly those mediated by viruses such as HIV, H1N1 influenza, and SARS-CoV-2. The SARS-CoV-2 infection causes the coronavirus disease 2019 (COVID-19) and it is responsible for the pandemic that we are currently living. COVID-19 causes an aggressive immune response known as cytokine release syndrome or cytokine storm that causes multiorgan failure and in most cases leads to death. In the present work, we aimed to review the molecular mechanisms by which obesity-associated systemic inflammation could cause a more severe clinical presentation of COVID-19. The SARS-CoV-2 infection could potentiate or accelerate the pre-existing systemic inflammatory state of individuals with obesity, via the NLRP3 inflammasome activation and the release of pro-inflammatory cytokines from cells trough Gasdermin-pores commonly found in cell death by pyroptosis.

Nonlinear dose-time-response functions and health-protective exposure limits for inflammation-mediated diseases

Why have occupational safety regulations in the United States not been more successful in protecting worker health from mesothelioma risks, while apparently succeeding relatively well in reducing silicosis risks? This paper briefly discusses biological bases for thresholds and nonlinearities in exposure-response functions for respirable crystalline silica (RCS) and asbestos, based on modeling a chronic inflammation mode of action (mediated by activation of the NLRP3 inflammasome, for both RCS and asbestos). It applies previously published physiologically based pharmacokinetic (PBPK) models to perform computational experiments illuminating how different time courses of exposure with the same time-weighted average (TWA) concentration affect internal doses in target tissues (lung for RCS and mesothelium for asbestos). Key conclusions are that (i) For RCS, but not asbestos, limiting average (TWA) exposure concentrations also tightly constrains internal doses and ability to trigger chronic inflammation and resulting increases in disease risks (ii) For asbestos, excursions (i.e., spikes in concentrations); and especially the times between them are crucial drivers of internal doses and time until chronic inflammation; and hence (iii) These dynamic aspects of exposure, which are not addressed by current occupational safety regulations, should be constrained to better protect worker health. Adjusting permissible average exposure concentration limits (PELs) and daily excursion limits (ELs) is predicted to have little impact on reducing mesothelioma risks, but increasing the number of days between successive excursions is predicted to be relatively effective in reducing worker risks, even if it has little or no impact on TWA average concentrations.

Dose-response modeling of NLRP3 inflammasome-mediated diseases: asbestos, lung cancer, and malignant mesothelioma as examples

Can a single fiber of amphibole asbestos increase the risk of lung cancer or malignant mesothelioma (MM)? Traditional linear no-threshold (LNT) risk assessment assumptions imply that the answer is yes: there is no safe exposure level. This paper draws on recent scientific progress in inflammation biology, especially elucidation of the activation thresholds for NLRP3 inflammasomes and resulting chronic inflammation, to model dose-response relationships for malignant mesothelioma and lung cancer risks caused by asbestos exposures. The modeling integrates a physiologically based pharmacokinetics (PBPK) front end with inflammation-driven two-stage clonal expansion (I-TSCE) models of carcinogenesis to describe how exposure leads to chronic inflammation, which in turn promotes carcinogenesis. Together, the combined PBPK and I-TSCE modeling predict that there are practical thresholds for exposure concentration below which asbestos exposure does not cause chronic inflammation in less than a lifetime, and therefore does not increase chronic inflammation-dependent cancer risks. Quantitative examples using model parameter estimates drawn from the literature suggest that practical thresholds may be within about a factor of 2 of some past exposure levels for some workers. The I-TSCE modeling framework explains previous puzzling aspects of asbestos epidemiology, such as why age at first exposure is a better predictor of lifetime MM risk than exposure duration. It may be a valuable tool for risk analysts when LNT assumptions are not justified due to inflammation response thresholds mediating dose-response relationships.

Expression of XBP1s in peritoneal mesothelial cells is critical for inflammation-induced peritoneal fibrosis

Intraperitoneal inflammation is the most important determinant of peritoneal fibrosis in patients with long-term peritoneal dialysis (PD). Spliced x-box binding protein-1 (XBP1s), a major proximal effector of unfolded protein response (UPR) signaling, plays an indispensable role in inflammation. Our study demonstrated that the inflammatory factor interleukin-1β (IL-1β) dose- and time-dependently induced XBP1s upregulation and interleukin-6 (IL-6) secretion, as well as the expression of the fibrotic marker fibronectin. However, these effects were prevented by the IRE1 endonuclease inhibitor STF083010 since it time-dependently reduced IL-1β-induced Xbp1 mRNA splicing, XBP1s protein expression, inflammatory factor IL-6 secretion and the expression of the fibrotic marker fibronectin in human peritoneal mesothelial cells (HPMCs). The overexpression and knockdown of XBP1s in HPMCs had a similar effect on fibronectin expression. In a rat model of peritoneal inflammation, STF083010 significantly attenuated chlorhexidine digluconate-induced XBP1s and α-smooth muscle actin expression, as well as fibrotic tissue proliferation, in the peritoneum. Our results suggest that XBP1s is a strong pathogenic factor that mediates inflammation-induced peritoneal fibrosis in peritoneal dialysis.

Pleural mesothelioma and lung cancer: the role of asbestos exposure and genetic variants in selected iron metabolism and inflammation genes

Two of the major cancerous diseases associated with asbestos exposure are malignant pleural mesothelioma (MPM) and lung cancer (LC). In addition to asbestos exposure, genetic factors have been suggested to be associated with asbestos-related carcinogenesis and lung genotoxicity. While genetic factors involved in the susceptibility to MPM were reported, to date the influence of individual genetic variations on asbestos-related lung cancer risk is still poorly understood. Since inflammation and disruption of iron (Fe) homeostasis are hallmarks of asbestos exposure affecting the pulmonary tissue, this study aimed at investigating the association between Fe-metabolism and inflammasome gene variants and susceptibility to develop LC or MPM, by comparing an asbestos-exposed population affected by LC with an "asbestos-resistant exposed population". A retrospective approach similar to our previous autopsy-based pilot study was employed in a novel cohort of autoptic samples, thus giving us the possibility to corroborate previous findings obtained on MPM by repeating the analysis in a novel cohort of autoptic samples. The protective role of HEPH coding SNP was further confirmed. In addition, the two non-coding SNPs, either in FTH1 or in TF, emerged to exert a similar protective role in a new cohort of LC exposed individuals from the same geographic area of MPM subjects. No association was found between NLRP1 and NLRP3 polymorphisms with susceptibility to develop MPM and LC. Further research into a specific MPM and LC "genetic signature" may be needed to broaden our knowledge of the genetic landscape attributed to result in MPM and LC.

Synthetic hydrosilicate nanotubes induce low pro-inflammatory and cytotoxic responses compared to natural chrysotile in lung cell cultures

Asbestos (Mg-hydrosilicate; chrysotile) is known to cause pleural diseases, pulmonary fibrosis and lung cancers, via mechanisms strongly depending on diameter-length ratio and possibly metal content. A critical question is whether synthetic hydrosilicate nanotubes (NTs) of short length possess little toxic potential compared to chrysotile. Five Mg- and two NiNTs of different lengths were assessed for cytotoxicity and pro-inflammatory responses in THP-1 macrophages and human bronchial epithelial lung cells (HBEC3-KT), in comparison with chrysotile. NT lengths/diameters were characterized by TEM, surface areas by BET- and BJH analysis, and chemical composition by XRD. The different Mg- and NiNTs induced little cytotoxicity in both cell models, in contrast to chrysotile that induced marked cytotoxicity. The two longest synthetic MgNTs, with median lengths of 3 and 5 µm, induced increased levels of pro-inflammatory cytokines in THP-1 macrophages, but much less than chrysotile (median length 15 µm) and silica nanoparticles (Si10). The shortest NTs did not induce any increase in cytokines. In HBEC3-KT cells, all synthetic NTs induced no or only small changes in cytokine responses, in contrast to chrysotile and Si10. The synthetic NTs induced lower TGF-β responses than chrysotile in both cell models. In conclusion, the pro-inflammatory responses were associated with the length of synthetic hydrosilicate NTs in THP-1 macrophages, but not in HBEC3-KT cells. Notably, the shortest NTs showed no or little pro-inflammatory activity or cytotoxicity in both cell models. Such a safety by design approach is important for development of new materials being candidates for various new products.

NLRP inflammasome as a key role player in the pathogenesis of environmental toxicants

Exposure to environmental toxicants (ET) results in specific organ damage and auto-immune diseases, mostly mediated by inflammatory responses. The NLRP3 inflammasome has been found to be the major initiator of the associated pathologic inflammation. It has been found that ETs can trigger all the signals required for an NLRP3-mediated response. The exaggerated activation of the NLRP3 inflammasome and its end product IL-1β, is responsible for the pathogenesis caused by many ETs including pesticides, organic pollutants, heavy metals, and crystalline compounds. Therefore, an extensive study of these chemicals and their mechanisms of inflammasome (INF) activation may provide the scientific evidence for possible targeting of this pathway by proposing possible protective agents that have been previously shown to affect INF compartments and its activation. Melatonin and polyunsaturated fatty acids (PUFA) are among the safest and the most studied of these agents, which affect a wide variety of cellular and physiological processes. These molecules have been shown to suppress the NLRP3 inflammasome mostly through the regulation of cellular redox status and the nuclear factor-κB (NF-κB) pathway, rendering them potential promising compounds to overcome ET-mediated organ damage. In the present review, we have made an effort to extensively review the ETs that exert their pathogenesis via the stimulation of inflammation, their precise mechanisms of action and the possible protective agents that could be potentially used to protect against such toxicants.

In Silico Transcriptomic Analysis of Wound-Healing-Associated Genes in Malignant Pleural Mesothelioma

Background and objectives: Malignant pleural mesothelioma (MPM) is a devastating malignancy with poor prognosis. Reliable biomarkers for MPM diagnosis, monitoring, and prognosis are needed. The aim of this study was to identify genes associated with wound healing processes whose expression could serve as a prognostic factor in MPM patients. Materials and Methods: We used data mining techniques and transcriptomic analysis so as to assess the differential transcriptional expression of wound-healing-associated genes in MPM. Moreover, we investigated the potential prognostic value as well as the functional enrichments of gene ontologies relative to microRNAs (miRNAs) of the significantly differentially expressed wound-healing-related genes in MPM. Results: Out of the 82 wound-healing-associated genes analyzed, 30 were found significantly deregulated in MPM. Kaplan–Meier analysis revealed that low ITGAV gene expression could serve as a prognostic factor favoring survival of MPM patients. Finally, gene ontology annotation enrichment analysis pointed to the members of the hsa-miR-143, hsa-miR-223, and the hsa-miR-29 miRNA family members as important regulators of the deregulated wound healing genes. Conclusions: 30 wound-healing-related genes were significantly deregulated in MPM, which are potential targets of hsa-miR-143, hsa-miR-223, and the hsa-miR-29 miRNA family members. Out of those genes, ITGAV gene expression was a prognostic factor of overall survival in MPM. Our results highlight the role of impaired tissue repair in MPM development and should be further validated experimentally.

Mesothelium and Malignant Mesothelioma

The mesothelium is an epithelial structure derived from the embryonic mesoderm. It plays an important role in the development of a number of different organs, including the heart, lungs, and intestines. In this publication, we discuss aspects of the development of the mesothelium, where mesothelial structures can be found, and review molecular and cellular characteristics associated with the mesothelium. Furthermore, we discuss the involvement of the mesothelium in a number of disease conditions, in particular in the pathogenesis of mesotheliomas with an emphasis on malignant pleural mesothelioma (MPM)—a primary cancer developing in the pleural cavity.

Malignant mesothelioma diagnosed at a younger age is associated with heavier asbestos exposure

Asbestos exposure is the main etiology of malignant mesothelioma, but there are conflicting data on whether the intensity of exposure modulates the development of this disease. This study considered 594 patients with malignant mesothelioma for whom count data on asbestos bodies and fibers (per gram of wet lung tissue) were available. The relationships between age at diagnosis (a time-to-event outcome variable) and these two measures of internal asbestos exposure, along with other possible modulating factors (sex, tumor location, histological subtype and childhood exposure), were assessed on multivariable Cox proportional hazard models, stratifying by decade of birth year. For both measures of asbestos in lung tissue, younger age at diagnosis was associated with higher internal measures of exposure to asbestos. Stratified Cox analyses showed that for each doubling in asbestos body count patients were 1.07 times more likely to be diagnosed at a younger age [hazard ratio (HR) = 1.07; 95% confidence interval (CI), 1.04-1.09; P = 2.2 × 10-7] and for each doubling in asbestos fiber count patients were 1.13 times more likely to be diagnosed at a younger age (HR = 1.13; 95% CI, 1.09-1.17; P = 8.6 × 10-11). None of the other variables considered were associated with age at diagnosis. Our finding that tumors become clinically apparent at a younger age in heavily exposed subjects suggests that asbestos is involved not only in the malignant mesothelioma tumor initiation but, somehow, also in the progression of the disease.

Biological mechanisms of non-linear dose-response for respirable mineral fibers

Sufficiently high and prolonged inhalation exposures to some respirable elongated mineral particles (REMPs), notably including amphibole asbestos fibers, can increase risk of inflammation-mediated diseases including malignant mesothelioma, pleural diseases, fibrosis, and lung cancer. Chronic inflammation involves ongoing activation of the NLRP3 inflammasome, which enables immune cells to produce potent proinflammatory cytokines IL-1β and IL-18. Reactive oxygen species (ROS) (in particular, mitochondrial ROS) contribute to NRLP3 activation via a well-elucidated mechanism involving oxidation of reduced thioredoxin and association of thioredoxin-interacting protein with NLRP3. Lysosomal destabilization, efflux of cytosolic potassium ions and influx of calcium ions, signals from damaged mitochondria, both translational and post-translational controls, and prion-like polymerization have increasingly clear roles in regulating NLRP3 activation. As the molecular biology of inflammation-mediated responses to REMP exposure becomes clearer, a practical question looms: What do these mechanisms imply for the shape of the dose-response function relating exposure concentrations and durations for EMPs to risk of pathological responses? Dose-response thresholds or threshold-like nonlinearities can arise from (a) Cooperativity in assembly of supramolecular signaling complexes; (b) Positive feedback loops and bistability in regulatory networks; (c) Overwhelming of defensive barriers maintaining homeostasis; and (d) Damage thresholds, as in lysosome destabilization-induced activation of NLRP3. Each of these mechanisms holds for NLRP3 activation in response to stimuli such as REMP exposures. It is therefore timely to consider the implications of these advances in biological understanding for human health risk assessment with dose-response thresholds.

Mouse serum exosomal proteomic signature in response to asbestos exposure

Asbestos-induced diseases like fibrosis and mesothelioma are very aggressive, without any treatment options. These diseases are diagnosed only at the terminal stages due to lack of early stage biomarkers. The recent discovery of exosomes as circulating biomarkers led us to look for exosomal biomarkers of asbestos exposure in mouse blood. In our model, mice were exposed to asbestos as a single bolus dose by oropharyngeal aspiration. Fifty-six days later blood was collected, exosomes were isolated from plasma and characterized and subjected to proteomic analysis using Tandem Mass Tag labeling. We identified many proteins, some of which were more abundant in asbestos exposed mouse serum exosomes, and three selected proteins were validated by immunoblotting. Our study is the first to show that serum exosomal proteomic signatures can reveal some important proteins relevant to asbestos exposure that have the potential to be validated as candidate biomarkers. We hope to extrapolate the positive findings of this study to humans in future studies.

New Perspectives on Diagnosis and Therapy of Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare, but severe form of cancer, with an incidence that varies significantly within and among different countries around the world. It develops in about one to two persons per million of the general population, leading to thousands of deaths every year worldwide. To date, the MPM is mostly associated with occupational asbestos exposure. Asbestos represents the predominant etiological factor, with approximately 70% of cases of MPM with well-documented occupational exposure to asbestos, with the exposure time, on average greater than 40 years. Environmental exposure to asbestos is increasingly becoming recognized as a cause of mesothelioma, together with gene mutations. The possible roles of other cofactors, such as viral infection and radiation exposure, are still debated. MPM is a fatal tumor. This cancer arises during its early phase without clinical signs. Consequently, its diagnosis occurs at advanced stages. Standard clinical therapeutic approaches include surgery, chemo- and radiotherapies. Preclinical and clinical researches are making great strides in the field of this deadly disease, identifying new biomarkers and innovative therapeutic approaches. Among the newly identified markers and potential therapeutic targets, circulating microRNAs and the Notch pathway represent promising avenues that could result in the early detection of the tumor and novel therapeutic approaches.

Exosomes from asbestos-exposed cells modulate gene expression in mesothelial cells

Asbestos exposure is a determinate cause of many diseases, such as mesothelioma, fibrosis, and lung cancer, and poses a major human health hazard. At this time, there are no identified biomarkers to demarcate asbestos exposure before the presentation of disease and symptoms, and there is only limited understanding of the underlying biology that governs asbestos-induced disease. In our study, we used exosomes, 30-140 nm extracellular vesicles, to gain insight into these knowledge gaps. As inhaled asbestos is first encountered by lung epithelial cells and macrophages, we hypothesize that asbestos-exposed cells secrete exosomes with signature proteomic cargo that can alter the gene expression of mesothelial cells, contributing to disease outcomes like mesothelioma. In the present study using lung epithelial cells (BEAS2B) and macrophages (THP-1), we first show that asbestos exposure causes changes in abundance of some proteins in the exosomes secreted from these cells. Furthermore, exposure of human mesothelial cells (HPM3) to these exosomes resulted in gene expression changes related to epithelial-to-mesenchymal transition and other cancer-related genes. This is the first report to indicate that asbestos-exposed cells secrete exosomes with differentially abundant proteins and that those exosomes have a gene-altering effect on mesothelial cells.-Munson, P., Lam, Y.-W., Dragon, J. MacPherson, M., Shukla, A. Exosomes from asbestos-exposed cells modulate gene expression in mesothelial cells.

Extracellular signal regulated kinase 5 and inflammasome in progression of mesothelioma

Malignant mesothelioma is an aggressive cancer in desperate need of treatment. We have previously shown that extracellular signaling regulated kinase 5 (ERK5) plays an important role in mesothelioma pathogenesis using ERK5 silenced human mesothelioma cells exhibiting significantly reduced tumor growth in immunocompromised mice. Here, we used a specific ERK 5 inhibitor, XMD8-92 in various in vitro and in vivo models to demonstrate that inhibition of ERK5 can slow down mesothelioma tumorigenesis. First, we show a dose dependent toxicity of XMD8-92 to 2 human mesothelioma cell lines growing as a monolayer. We also demonstrate the inhibition of ERK5 phosphorylation in various human mesothelioma cell lines by XMD8-92. We further confirmed the toxicity of XMD8-92 towards mesothelioma cell lines grown as spheroids in a 3-D model as well as in intraperitoneal (immune-competent) and intrapleural (immune-deficient) mouse models with and without chemotherapeutic drugs. To ascertain the mechanism, we explored the role of the nod-like receptor family member containing a pyrin domain 3 (NLRP3) inflammasome in the process. We found XMD8-92 attenuated naïve and chemotherapeutic-induced inflammasome priming and activation in mesothelioma cells. It can thus be concluded that ERK5 inhibition attenuates mesothelioma tumor growth and this phenomenon in part is regulated by the inflammasome.

The Synthetic Lignan Secoisolariciresinol Diglucoside Prevents Asbestos-Induced NLRP3 Inflammasome Activation in Murine Macrophages

BACKGROUND

The interaction of asbestos with macrophages drives two key processes that are linked to malignancy: (1) the generation of reactive oxygen species (ROS)/reactive nitrogen species (RNS) and (2) the activation of an inflammation cascade that drives acute and chronic inflammation, with the NLRP3 inflammasome playing a key role. Synthetic secoisolariciresinol diglucoside (SDG), LGM2605, is a nontoxic lignan with anti-inflammatory and antioxidant properties and was evaluated for protection from asbestos in murine peritoneal macrophages (MF).

METHODS

MFs were exposed to crocidolite asbestos ± LGM2605 given 4 hours prior to exposure and evaluated at various times for NLRP3 expression, secretion of inflammasome-activated cytokines (IL-1β and IL-18), proinflammatory cytokines (IL-6, TNFα, and HMGB1), NF-κB activation, and levels of total nitrates/nitrites.

RESULTS

Asbestos induces a significant (p < 0.0001) increase in the NLRP3 subunit, release of proinflammatory cytokines, NLRP3-activated cytokines, NF-κB, and levels of nitrates/nitrites. LGM2605 significantly reduced NLRP3 ranging from 40 to 81%, IL-1β by 89-96%, and TNFα by 67-78%, as well as activated NF-κB by 48-49% while decreasing levels of nitrates/nitrites by 85-93%.

CONCLUSIONS

LGM2605 reduced asbestos-induced NLRP3 expression, proinflammatory cytokine release, NF-κB activation, and nitrosative stress in MFs supporting its possible use in preventing the asbestos-induced inflammatory cascade leading to malignancy.

Inflammasomes and Cancer: The Dynamic Role of the Inflammasome in Tumor Development

Chronic Inflammation in tumor microenvironments is not only associated with various stages of tumor development, but also has significant impacts on tumor immunity and immunotherapy. Inflammasome are an important innate immune pathway critical for the production of active IL-1β and interleukin 18, as well as the induction of pyroptosis. Although extensive studies have demonstrated that inflammasomes play a vital role in infectious and autoimmune diseases, their role in tumor progression remains elusive. Multiple studies using a colitis-associated colon cancer model show that inflammasome components provide protection against the development of colon cancer. However, very recent studies demonstrate that inflammasomes promote tumor progression in skin and breast cancer. These results indicate that inflammasomes can promote and suppress tumor development depending on types of tumors, specific inflammasomes involved, and downstream effector molecules. The complicated role of inflammasomes raises new opportunities and challenges to manipulate inflammasome pathways in the treatment of cancer.

Targeting the epigenome in malignant pleural mesothelioma

Malignant pleural mesotheliomas (MPM) are notoriously refractory to conventional treatment modalities. Recent insights regarding epigenetic alterations in MPM provide the preclinical rationale for the evaluation of novel combinatorial regimens targeting the epigenome in these neoplasms.