Cellular and molecular mechanisms of asbestos-induced fibrosis

Cyclophilin A accelerates SiO2-induced macrophage foaming

Silicosis is a common occupational disease characterized by lung inflammation, fibrosis and pulmonary dysfunction caused by long-term inhalation of free SiO₂. Cell foaming and the change of CyPA have been observed in SiO₂-induced macrophages, but the specific mechanism of CyPA in SiO₂-induced foam cells remains poorly understood. The purpose of this study is to explore the mechanism of CyPA in SiO₂-induced macrophage foaming and its effect on silicosis. We found that overexpression of CyPA promoted the macrophage foaming and the expression of COL I and α-SMA, while silencing CyPA inhibites the macrophage foaming and the expression of COL I and α-SMA. After blocking the expression of CD36 on the basis of overexpression CyPA, we found it inhibites the macrophage foaming. In conclusion, CyPA can affect the foaming of macrophages and may participate in silicosis fibrosis.

Asbestos Exposure and Severity of COVID-19

BACKGROUND

The aim of this study was to analyse the relationship between occupational exposure to asbestos and the severity of SARS-CoV-2 infection.

METHODS

We evaluated patients who survived admission in our centre for COVID-19 pneumonia. Demographic, analytical, and clinical variables were collected during admission. After discharge, a previously validated occupational exposure to asbestos questionnaire was administered. Spirometry, CO diffusion test, the 6-min walk test, and high-resolution chest CT were performed. Patients who required respiratory support (oxygen, CPAP, or NIV) were considered severe.

RESULTS

In total, 293 patients (mean age 54 + 13 years) were included. Occupational exposure to asbestos was detected in 67 (24%). Patients with occupational exposure to asbestos had a higher frequency of COVID-19 pneumonia requiring respiratory support (n = 52, 77.6%) than their unexposed peers (n = 139, 61.5%) (p = 0.015). Asbestos exposure was associated with COVID-19 severity in the univariate but not in the multivariate analysis. No differences were found regarding follow-up variables including spirometry and the DLCO diffusion, the 6-min walk test, and CT alterations.

CONCLUSIONS

In hospitalised patients with COVID-19 pneumonia, those with occupational exposure to asbestos more frequently needed respiratory support. However, an independent association between asbestos exposure and COVID-19 severity could not be confirmed.

Fibrosis in Mesothelioma: Potential Role of Lysyl Oxidases

Immunotherapies (such as checkpoint inhibitors) and standard chemotherapies (such as cisplatin) have limitations in the successful treatment of malignant pleural mesothelioma (MPM). Fibrosis is the accumulation of collagen in the extracellular matrix (ECM) of tissues, making them denser than that of healthy tissues and thereby affecting drug delivery and immune cell infiltration. Moreover, fibrosis severely affects the patient's breathing and quality of life. The production of collagen and its assembly is highly regulated by various enzymes such as lysyl oxidases. Many solid tumors aberrantly express the family of lysyl oxidases (LOX/LOXL). This review examines how LOX/LOXLs were found to be dysregulated in noncancerous and cancerous settings, discusses their roles in solid tumor fibrosis and pathogenesis and explores the role of fibrosis in the development and poor clinical outcomes of patients with MPM. We examine the current preclinical status of drugs targeting LOX/LOXLs and how the incorporation of such drugs may have therapeutic benefits in the treatment and management of patients with MPM.

Metformin Attenuates Silica-Induced Pulmonary Fibrosis by Activating Autophagy via the AMPK-mTOR Signaling Pathway

Long-term exposure to crystalline silica particles leads to silicosis characterized by persistent inflammation and progressive fibrosis in the lung. So far, there is no specific treatment to cure the disease other than supportive care. In this study, we examined the effects of metformin, a prescribed drug for type || diabetes on silicosis and explored the possible mechanisms in an established rat silicosis model in vivo, and an in vitro co-cultured model containing human macrophages cells (THP-1) and human bronchial epithelial cells (HBEC). Our results showed that metformin significantly alleviated the inflammation and fibrosis of lung tissues of rats exposed to silica particles. Metformin significantly reduced silica particle-induced inflammatory cytokines including transforming growth factor-β1 (TGF-β1), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in rat lung tissue and HBEC culture supernatant. The protein levels of Vimentin and α-smooth muscle actin (α-SMA) were significantly decreased by metfomin while expression level of E-cadherin (E-Cad) increased. Besides, metformin increased the expression levels of phosphorylated adenosine 5′-monophosphate (AMP)-activated protein kinase (p-AMPK), microtubule-associated protein (MAP) light chain 3B (LC3B) and Beclin1 proteins, and reduced levels of phosphorylated mammalian target of rapamycin (p-mTOR) and p62 proteins in vivo and in vitro. These results suggest that metformin could inhibit silica-induced pulmonary fibrosis by activating autophagy through the AMPK-mTOR pathway.

Molecular Fingerprints of Malignant Pleural Mesothelioma: Not Just a Matter of Genetic Alterations

Malignant pleural mesothelioma (MPM) is a clinical emergency of our time. Being strongly associated with asbestos exposure, incidence of this cancer is ramping up these days in many industrialized countries and it will soon start to increase in many developing areas where the use of this silicate derivate is still largely in use. Deficiency of reliable markers for the early identification of these tumors and the limited efficacy of the currently available therapeutic options are the basis of the impressive mortality rate of MPM. These shortcomings reflect the very poor information available about the molecular basis of this disease. Results of the recently released deep profiling studies point to the epigenome as a central element in MPM development and progression. First, MPM is characterized by a low mutational burden and a highly peculiar set of mutations that hits almost exclusively epigenetic keepers or proteins controlling chromatin organization and function. Furthermore, asbestos does not seem to be associated with a distinctive mutational signature, while the precise mapping of epigenetic changes caused by this carcinogen has been defined, suggesting that alterations in epigenetic features are the driving force in the development of this disease. Last but not least, consistent evidence also indicates that, in the setting of MPM, chromatin rewiring and epigenetic alterations of cancer cells heavily condition the microenvironment, including the immune response. In this review we aim to point to the relevance of the epigenome in MPM and to highlight the dependency of this tumor on chromatin organization and function. We also intend to discuss the opportunity of targeting these mechanisms as potential therapeutic options for MPM.

Genomics and Epigenetics of Malignant Mesothelioma

Malignant mesothelioma is an aggressive and lethal asbestos-related disease. Diagnosis of malignant mesothelioma is particularly challenging and is further complicated by the lack of disease subtype-specific markers. As a result, it is especially difficult to distinguish malignant mesothelioma from benign reactive mesothelial proliferations or reactive fibrosis. Additionally, mesothelioma diagnoses can be confounded by other anatomically related tumors that can invade the pleural or peritoneal cavities, collectively resulting in delayed diagnoses and greatly affecting patient management. High-throughput analyses have uncovered key genomic and epigenomic alterations driving malignant mesothelioma. These molecular features have the potential to better our understanding of malignant mesothelioma biology as well as to improve disease diagnosis and patient prognosis. Genomic approaches have been instrumental in identifying molecular events frequently occurring in mesothelioma. As such, we review the discoveries made using high-throughput technologies, including novel insights obtained from the analysis of the non-coding transcriptome, and the clinical potential of these genetic and epigenetic findings in mesothelioma. Furthermore, we aim to highlight the potential of these technologies in the future clinical applications of the novel molecular features in malignant mesothelioma.

Oxidative and cytotoxic stress induced by inorganic granular and fibrous particles

The hazards of granular and fibrous particles have been associated with the generation of reactive oxygen species (ROS), which in turn is often associated with physicochemical properties exhibited by these particles. In the present study, the ability of various types of fibrous and granular dusts to generate oxidative stress, and their cytotoxicity, was investigated. Biopersistent granular dusts employed in the present study included micro‑ and nanosized titanium dioxide with rutile or anatase crystal structure modifications. Additionally, glass fibres, chrysotile and crocidolite asbestos representative of fibrous dust were selected. Detailed characterisation of particles was performed using scanning electron microscopy, and the effect of exposure to these particles on cell viability and intracellular ROS generation was assessed by PrestoBlue and 2',7'‑dichlorofluorescein assays, respectively. A549 human lung epithelial adenocarcinoma cells were exposed to increasing concentrations (0.1‑10 µg/cm2) of particles and fibres for 24 h. Subsequently, the gene expression of X‑linked inhibitor of apoptosis (XIAP), superoxide dismutase (SOD)1 and SOD2 were analysed by reverse transcription‑quantitative polymerase chain reaction. All investigated granular particles induce ROS production in A549 lung carcinoma cells within 24 h. Hematite increased ROS production in a dose‑dependent manner. A concentration of >1 µg/cm2 TiO2 na with its disordered surface, demonstrated the greatest ability to generate ROS. Therefore, the crystalline surface structure of the particle may be considered as a determinant of the extent of ROS induction by the particle. Fibrous particle compared with granular particles were associated with a lower ability to generate ROS. Glass fibres did not significantly increase ROS production in A549 cells, but elevated gene expression of SOD2 was observed. The results demonstrated that in general, the ability of particles to generate ROS depends on their number and crystal phase. Therefore, the present study helps to understand the cause of particle toxicity.

β1-Integrin Deletion From the Lens Activates Cellular Stress Responses Leading to Apoptosis and Fibrosis

Purpose

Previous research showed that the absence of β1-integrin from the mouse lens after embryonic day (E) 13.5 (β1MLR10) leads to the perinatal apoptosis of lens epithelial cells (LECs) resulting in severe microphthalmia. This study focuses on elucidating the molecular connections between β1-integrin deletion and this phenotype.

Methods

RNA sequencing was performed to identify differentially regulated genes (DRGs) in β1MLR10 lenses at E15.5. By using bioinformatics analysis and literature searching, Egr1 (early growth response 1) was selected for further study. The activation status of certain signaling pathways (focal adhesion kinase [FAK]/Erk, TGF-β, and Akt signaling) was studied via Western blot and immunohistochemistry. Mice lacking both β1-integrin and Egr1 genes from the lenses were created (β1MLR10/Egr1-/-) to study their relationship.

Results

RNA sequencing identified 120 DRGs that include candidates involved in the cellular stress response, fibrosis, and/or apoptosis. Egr1 was investigated in detail, as it mediates cellular stress responses in various cell types, and is recognized as an upstream regulator of numerous other β1MLR10 lens DRGs. In β1MLR10 mice, Egr1 levels are elevated shortly after β1-integrin loss from the lens. Further, pErk1/2 and pAkt are elevated in β1MLR10 LECs, thus providing the potential signaling mechanism that causes Egr1 upregulation in the mutant. Indeed, deletion of Egr1 from β1MLR10 lenses partially rescues the microphthalmia phenotype.

Conclusions

β1-integrin regulates the appropriate levels of Erk1/2 and Akt phosphorylation in LECs, whereas its deficiency results in the overexpression of Egr1, culminating in reduced cell survival. These findings provide insight into the molecular mechanism underlying the microphthalmia observed in β1MLR10 mice.

Evaluation of Dynamic Disulphide/Thiol Homeostasis in Silica Exposed Workers

BACKGROUND

Oxidative stress is implicated as one of the main molecular mechanism underlying silicosis.

AIMS

In this study, our aim was to asses the redox status in occupationally silica-exposed workers, by evaluating the dynamic thiol-disulphide homeostasis.

STUDY DESIGN

Case-control study.

METHODS

Thirty-six male workers occupationally exposed to silica particles and 30 healthy volunteers, working as office workers were included to the study. Posteroanterior chest radiographs and pulmonary function tests of both groups were evaluated. Also serum thiol disulphide levels were measured using the spectrophotometric method described by Erel and Neşelioğlu.

RESULTS

Among the 36 workers that underwent pulmonary function tests 6 (17%) had obstructive, 7 (19%) had restrictive, 6 (17%) had obstructive and restrictive signs whereas 17 (47%) had no signs. The mean PFTs results of silica-exposed workers were significantly lower than control subjects. The serum disulphide levels of silica-exposed workers were significantly higher than control subjects (23.84±5.89 μmol/L and 21.18±3.44 μmol/L, respectively p=0.02).

CONCLUSION

The serum disulphide levels, a biomarker of oxidative stress, are found to be higher in silica-exposed workers.

Circulating levels of interleukin-18 in asbestos-exposed workers

Occupational exposure to asbestos has been associated with the development of pulmonary diseases through a persistent inflammatory response initiated by reactive oxygen species and the subsequent release of proinflammatory mediators such as interleukin (IL)-1, IL-6 and tumour necrosis factor (TNF)-a. Recently, IL-18, a pleiotropic proinflammatory cytokine and potent inducer of gene expression and synthesis of INF-g, TNF-a and IL-1 in immunocompetent cells, has been described. IL-18 serum concentrations were measured in 20 asbestos-exposed workers and in a group of 20 healthy donors. The workers underwent physical examination, pulmonary function tests and high-resolution computed tomography (HRCT). IL-18 levels were assayed in peripheral blood using the immunoenzymatic method with a commercial kit. The pulmonary function tests revealed a restrictive ventilatory deficit in nine (45%) cases and an obstructive ventilatory deficit in five (25%). The remaining six (30%) workers exhibited normal spirometric values. HRCT findings were: bilateral pleural plaques in 8 (40%) workers and bilateral parenchymal fibrosis in 12 (60%), with mean scores of 2.559 / 1.89. The exposed workers displayed significantly higher IL-18 concentrations than controls and those with parenchymal fibrosis displayed significantly higher values than workers with pleural plaques (P=0.001). In subjects with parenchymal fibrosis, HRCT scores significantly correlated with serum levels of IL-18 (P=0.001). Although the mechanisms leading to IL-18 release in asbestosis are unknown, the present preliminary results underscore the potential role of this cytokine in the pathogenesis of pulmonary toxicity.

Predicting pulmonary fibrosis in humans after exposure to multi-walled carbon nanotubes (MWCNTs)

The increased production and use of multi-walled carbon nanotubes (MWCNTs) in a diverse array of consumer, medical, and industrial applications have raised concerns about potential human exposure to these materials in the workplace and ambient environments. Inhalation is a primary route of exposure to MWCNTs, and the existing data indicate that they are potentially hazardous to human health. While a 90-day rodent inhalation test (e.g., OECD Test No. 413: subchronic inhalation toxicity: 90-day study or EPA Health Effects Test Guidelines OPPTS 870.3465 90-day inhalation toxicity) is recommended by the U.S. Environmental Protection Agency Office of Pollution Prevention and Toxics for MWCNTs (and other CNTs) if they are to be commercially produced (Godwin et al. in ACS Nano 9:3409-3417, 2015), this test is time and cost-intensive and subject to scientific and ethical concerns. As a result, there has been much interest in transitioning away from studies on animals and moving toward human-based in vitro and in silico models. However, given the multiple mechanisms of toxicity associated with subchronic exposure to inhaled MWCNTs, a battery of non-animal tests will likely be needed to evaluate the key endpoints assessed by the 90-day rodent study. Pulmonary fibrosis is an important adverse outcome related to inhalation exposure to MWCNTs and one that the non-animal approach should be able to assess. This review summarizes the state-of-the-science regarding in vivo and in vitro toxicological methods for predicting MWCNT-induced pulmonary fibrosis.

Citrate gold nanoparticle exposure in the marine bivalve Ruditapes philippinarum: uptake, elimination and oxidative stress response

Gold nanoparticles (AuNPs) are considered an important nano-sized component of the twenty-first century. Due to their unique physical and chemical properties, they are being used and developed for a wide range of promising applications in medicine, biology and chemistry. Notwithstanding their useful aspects, in recent years concern has been raised over their ability to enter cells, organelles and nuclei and provoke oxidative stress. In a laboratory-based experiment, the non-target marine bivalve Ruditapes philippinarum was used as a model organism. Uptake, elimination and molecular effects under short-term and sub-chronic exposure conditions to an environmental relevant concentration (0.75 μg L(-1)) of weakly agglomerating citrate AuNPs (∼20 nm) were studied. Our results demonstrate that at the tested concentration, the particles are readily taken up into the digestive gland > gills and can produce significant changes (p < 0.05) in oxidative stress and inflammatory response markers, as measured by phase II antioxidant enzymes and q-PCR gene expression analysis. However, the overall magnitude of responses was low, and oxidative damage was not provoked. Further, a significant elimination of Au from the digestive tract within a 7-day purification period was observed, with excretion being an important pathway. In conclusion, short-term and sub-chronic exposure to an environmental relevant concentration of citrate-stabilized AuNPs cannot be considered toxic to our model organism, while some further consideration should be given to chronic exposure effects.

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.

Mechanisms of toxicity by carbon nanotubes

Carbon nanotubes (CNTs) consist of a family of carbon built nanoparticles, whose biological effects depend on their physical characteristics and other constitutive chemicals (impurities and functions attached). CNTs are considered the twenty first century material due to their unique physicochemical characteristics and applicability to industrial product. The use of these materials steadily increases worldwide and toxic outcomes need to be studied for each nanomaterial in depth to prevent adverse effects to humans and the environment. Entrance into the body is physical, and usually few nanoparticles enter the body; however, once there, they are persistent due to their limited metabolisms, so their removal is slow, and chronic cumulative health effects are studied. Oxidative stress is the main mechanism of toxicity but size, agglomeration, chirality as well as impurities and functionalization are some of the structural and chemical characteristic contributing to the CNTs toxicity outcomes. Among the many toxicity pathways, interference with cytoskeleton and fibrous mechanisms, cell signaling, membrane perturbations and the production of cytokines, chemokines and inflammation are some of the effects resulting from exposure to CNTs. The aim of this review is to offer an up-to-date scope of the effects of CNTs on biological systems with attention to mechanisms of toxicity.

The Role of Nuclear Factor Kappa B in the Pathogenesis of Pulmonary Diseases: Implications for Therapy

The nuclear factor kappa B (NF-kappaB) transcription factor plays a key role in the induction of pro-inflammatory gene expression, leading to the synthesis of cytokines, adhesion molecules, chemokines, growth factors and enzymes. Results of studies in in vitro and in vivo models of inflammation and malignancy have also suggested central roles for NF-kappaB in programmed cell death, or apoptosis. NF-kappaB plays a central role in a variety of acute and chronic inflammatory diseases. In the common lung diseases associated with a significant inflammatory component such as severe sepsis, acute lung injury, acute respiratory distress syndrome, cystic fibrosis and asthma, the pathogenic roles of NF-kappaB have been extensively investigated. In COPD, activation of NF-kappaB has been implicated in disease pathogenesis but its exact role is less clearly demonstrable in this heterogeneous patient population. However, the principal risk factor for COPD, cigarette smoking, is strongly associated with NF-kappaB activation. Activation of NF-kappaB has been demonstrated in mineral dust diseases and probably plays a role in the pathogenesis of these chronic illnesses. NF-kB also plays a variety of roles in lung cancer including resistance to chemotherapy, inhibition of tumorigenesis and inducing expression of antiapoptotic genes. The complex NF-kappaB pathway offers a variety of potential molecular targets for chemotherapeutic intervention. A variety of agents aimed at modulating NF-kappaB activity are in various stages of investigation.

Adipokine adipsin is associated with the degree of lung fibrosis in asbestos-exposed workers

OBJECTIVES

Asbestos-exposure causes an inflammatory response driven by alveolar macrophages that can lead to pulmonary fibrosis. In addition to classical inflammatory cytokines, macrophages produce adipokines which regulate the inflammatory response. We studied if adipokines are related to the degree of parenchymal fibrosis, impaired lung function and inflammation in asbestos-exposed subjects.

METHODS

Eighty-five males with moderate to heavy occupational exposure to asbestos and unexposed controls were studied. We measured plasma levels of adipokines adiponectin, adipsin, leptin and resistin, IL-6, IL-8, erythrocyte sedimentation rate (ERS), spirometry and D(L,CO). Degree of interstitial lung fibrosis (septal thickening, subpleural lines, parenchymal bands or honeycombing) was scored in classes 0-5 according to a validated scoring system. The subjects were divided into three groups: normal parenchymal finding (fibrosis class 0), borderline changes (classes 0.5-1.5) and fibrosis (i.e. asbestosis; classes 2-5).

RESULTS

Adipsin correlated positively with parenchymal fibrosis (rho=0.412, p<0.001) and there was a linear increasing trend of mean plasma adipsin levels among the three groups of asbestos-exposed subjects (from normal parenchymal finding to borderline changes and to fibrosis) (p<0.0001). Accordingly, plasma adipsin levels correlated positively with the extent of pleural plaques (r=0.245, p=0.043), and negatively with D(L,CO) (r=-0.246, p=0.023). Also, a positive correlation was found between adipsin and inflammatory markers ESR (r=0.315, p=0.008) and IL-6 (r=0.256, p=0.018).

CONCLUSIONS

Adipsin was associated with the degree of parenchymal fibrosis, impairment of pulmonary diffusing capacity and with inflammatory activity in asbestos-exposed subjects suggesting that adipsin may have a role in the pathogenesis or as a biomarker in asbestos-induced lung disease.

Evaluation of tremolite asbestos exposures associated with the use of commercial products

Tremolite is a noncommercial form of amphibole mineral that is present in some chrysotile, talc, and vermiculite deposits. Inhalation of asbestiform tremolite is suspected to have caused or contributed to an increased incidence of mesothelioma in certain mining settings; however, very little is known about the magnitude of tremolite exposure that occurred at these locations, and even less is known regarding tremolite exposures that might have occurred during consumer use of chrysotile, talc, and vermiculite containing products. The purpose of this analysis is to evaluate the exposure-response relationship for tremolite asbestos and mesothelioma in high exposure settings (mining) and to develop estimates of tremolite asbestos exposure for various product use scenarios. Our interpretation of the tremolite asbestos exposure metrics reported for the Thetford chrysotile mines and the Libby vermiculite deposits suggests a lowest-observed-adverse-effect level (LOAEL) for mesothelioma of 35-73 f/cc-year. Using measured and estimated airborne tremolite asbestos concentrations for simulated and actual product use, we conservatively estimated the following cumulative tremolite asbestos exposures: career auto mechanic: 0.028 f/cc-year; non-occupational use of joint compound: 0.0006 f/cc-year; non-occupational use of vermiculite-containing gardening products: 0.034 f/cc-year; home-owner removal of Zonolite insulation: 0.0002 f/cc-year. While the estimated consumer tremolite exposures are far below the tremolite LOAELs derived herein, this analysis examines only a few of the hundreds of chrysotile- and talc-containing products.

Mechanisms of crystalline silica-induced pulmonary toxicity revealed by global gene expression profiling

A proper understanding of the mechanisms underlying crystalline silica-induced pulmonary toxicity has implications in the management and potential prevention of the adverse health effects associated with silica exposure including silicosis, cancer and several auto-immune diseases. Human lung type II epithelial cells and rat lungs exposed to crystalline silica were employed as experimental models to determine global gene expression changes in order to understand the molecular mechanisms underlying silica-induced pulmonary toxicity. The differential gene expression profile induced by silica correlated with its toxicity in the A549 cells. The biological processes perturbed by silica exposure in the A549 cells and rat lungs, as identified by the bioinformatics analysis of the differentially expressed genes, demonstrated significant similarity. Functional categorization of the differentially expressed genes identified cancer, cellular movement, cellular growth and proliferation, cell death, inflammatory response, cell cycle, cellular development, and genetic disorder as top ranking biological functions perturbed by silica exposure in A549 cells and rat lungs. Results of our study, in addition to confirming several previously identified molecular targets and mechanisms involved in silica toxicity, identified novel molecular targets and mechanisms potentially involved in silica-induced pulmonary toxicity. Further investigations, including those focused on the novel molecular targets and mechanisms identified in the current study may result in better management and, possibly, reduction and/or prevention of the potential adverse health effects associated with crystalline silica exposure.

Onconase mediated NFKβ downregulation in malignant pleural mesothelioma

Purpose

Treatment of malignant pleural mesothelioma (MPM) with Ranpirnase (Onconase) results in disruption of protein translation and cell apoptosis. We hypothesize that Onconase acts via down regulation of nuclear factor kappa B (NFKβ) by specific microRNAs (miRNA) and that interference of this pathway could have implications for MPM resistance to chemotherapy.

Experimental Design

Three immortalized MPM cell lines (H2959, H2373, and H2591) were exposed to Onconase at 0–20 µg/mL. Cell counts were measured at 48 and 72 hours. Gene expression in miRNA-enriched RNA was validated by RT-PCR. The functional implications of miRNA expression were evaluated by transfecting miRNA mimics or inhibitors into MPM cell lines, and performing Matrigel™ invasion, cell proliferation, soft agar colony formation, and scratch closure assays. Effects on NFKβ expression and downstream targets including ABC transporters, BCL-xl, and IAP were assessed by RT-PCR and Western Blotting.

Results

Treatment with 20µg/mL of Onconase significantly decreased cell count and invasion. Hsa-miR-17* was significantly upregulated and hsa-miR-30c significantly down-regulated by Onconase treatment in all cell lines. Forced expression of hsa-miR-17* mimic and hsa-miR-30c inhibitor each significantly decreased functional activity of Onconase in all assays. NFKB1(p50) expression and downstream targets were also decreased with Onconase treatment as well as with forced expression miRNA mimic and inhibitors.

Conclusions

Onconase treatment caused a significant decrease in cell proliferation, invasion, and in expression of certain miRNAs. Recapitulation of the resultant miRNA expression pattern with hsa-miR-17* mimic and hsa-miR-30c inhibitor resulted in downregulation of NFKB1 and reduced malignant behavior in functional assays. Thus, Onconase likely exerts its anti-tumor effect through these miRNAs.

Pulmonary endpoints (lung carcinomas and asbestosis) following inhalation exposure to asbestos

Lung carcinomas and pulmonary fibrosis (asbestosis) occur in asbestos workers. Understanding the pathogenesis of these diseases is complicated because of potential confounding factors, such as smoking, which is not a risk factor in mesothelioma. The modes of action (MOA) of various types of asbestos in the development of lung cancers, asbestosis, and mesotheliomas appear to be different. Moreover, asbestos fibers may act differentially at various stages of these diseases, and have different potencies as compared to other naturally occurring and synthetic fibers. This literature review describes patterns of deposition and retention of various types of asbestos and other fibers after inhalation, methods of translocation within the lung, and dissolution of various fiber types in lung compartments and cells in vitro. Comprehensive dose-response studies at fiber concentrations inhaled by humans as well as bivariate size distributions (lengths and widths), types, and sources of fibers are rarely defined in published studies and are needed. Species-specific responses may occur. Mechanistic studies have some of these limitations, but have suggested that changes in gene expression (either fiber-catalyzed directly or by cell elaboration of oxidants), epigenetic changes, and receptor-mediated or other intracellular signaling cascades may play roles in various stages of the development of lung cancers or asbestosis.

Non-neoplastic and neoplastic pleural endpoints following fiber exposure

Exposure to asbestos fibers is associated with non-neoplastic pleural diseases including plaques, fibrosis, and benign effusions, as well as with diffuse malignant pleural mesothelioma. Translocation and retention of fibers are fundamental processes in understanding the interactions between the dose and dimensions of fibers retained at this anatomic site and the subsequent pathological reactions. The initial interaction of fibers with target cells in the pleura has been studied in cellular models in vitro and in experimental studies in vivo. The proposed biological mechanisms responsible for non-neoplastic and neoplastic pleural diseases and the physical and chemical properties of asbestos fibers relevant to these mechanisms are critically reviewed. Understanding mechanisms of asbestos fiber toxicity may help us anticipate the problems from future exposures both to asbestos and to novel fibrous materials such as nanotubes. Gaps in our understanding have been outlined as guides for future research.

Pulmonary inflammatory and fibrotic responses in Fischer 344 rats after intratracheal instillation exposure to Libby amphibole

Increased incidences of asbestosis have been reported in workers from Libby, MT, associated with exposures to amphibole-contaminated vermiculite. In this study pulmonary and histopathological changes were investigated following Libby amphibole (LA) exposure in a rat model. Rat respirable fractions of LA and amosite (aerodynamic diameter <2.5 μm) were prepared by water elutriation. Male F344 rats were exposed to single doses of either saline (SAL), amosite (0.65 mg/rat), or LA (0.65 or 6.5 mg/rat) by intratracheal instillation. At times from 1 d to 3 mo after exposure, bronchoalveolar lavage (BAL) was performed and right and left lungs were removed for reverse-transcription polymerase chain reaction (RT-PCR) and histopathological analysis, respectively. Data indicated that 0.65 mg amosite resulted in a higher degree of pulmonary injury, inflammation, and fibrotic events than LA at the same mass dose. Exposure to either amosite or high dose LA resulted in higher levels of cellular permeability and injury, inflammatory enzymes, and iron binding proteins in both BAL fluid and lung tissue at most time points when compared to SAL controls. However, mRNA expression for some growth factors (e.g., platelet-derived growth factor [PDGF]-A and transforming growth factor [TGF]-1β), which contribute to fibrosis, were downregulated at several time points. Furthermore, histopathological examination showed notable thickening of interstitial areas surrounding the alveolar ducts and terminal bronchioles. On a mass dose basis, amosite produced a greater acute and persistent lung injury for at least 3 mo after exposure. However, further testing and analysis of LA are needed with regard to the dose metric to fully evaluate its potential fibrogenicity and carcinogenicity.

Experience with peritoneal mesothelioma at the Milan National Cancer Institute

Diffuse malignant peritoneal mesothelioma (DMPM) is an uncommon and rapidly fatal tumor. Therapeutic options have traditionally been limited and ineffective. The biologic and molecular events correlated with poor responsiveness to therapy are still poorly understood. In recent years, an innovative treatment approach involving aggressive cytoreductive surgery (CRS) and perioperative intraperitoneal chemotherapy has reportedly resulted in improved outcome, as compared to historical controls. Since 1995, at the National Cancer Institute (NCI) of Milan (Italy), patients with DMPM have been treated with CRS and hyperthermic intra-peritoneal chemotherapy (HIPEC). In the present paper, clinical experiences and basic science investigations on DMPM at Milan NCI are reviewed. Peri-operative and long-term outcome results with CRS and HIPEC are presented. Clinico-pathological prognostic factors were investigated by multivariate analysis. The pathologic features and immunohistochemical markers related to DMPM biologic behavior were assessed in a large case-series uniformly treated at our institution. The prevalence and prognostic role of telomere maintenance mechanisms, which account for the limitless cell replicative potential of many malignancies, were studied. The dysregulation of the apoptotic pathways may play a role in the relative chemo-resistance of DMPM and a better understanding of apoptosis-related mechanisms could result in novel targeted therapeutic strategies. On this basis, the expression of survivin and other IAP family members (IAP-1, IAP-2, and X-IAP), the pro-apoptotic protein Smac/DIABLO, and antigens associated with cell proliferation (Ki-67) and apoptosis (caspase-cleaved cytokeratin-18) were analyzed. Finally, analyses of EGFR, PDGFRA and PDGFRB were performed to ascertain if deregulation of RTK could offer useful alternative therapeutic targets.

Utilization of gene profiling and proteomics to determine mineral pathogenicity in a human mesothelial cell line (LP9/TERT-1)

Identifying and understanding the early molecular events that underscore mineral pathogenicity using in vitro screening tests is imperative, especially given the large number of synthetic and natural fibers and particles being introduced into the environment. The purpose of the work described here was to examine the ability of gene profiling (Affymetrix microarrays) to predict the pathogenicity of various materials in a human mesothelial cell line (LP9/TERT-1) exposed to equal surface area concentrations (15 x 10(6) or 75 x 10(6) microm(2)/cm(2)) of crocidolite asbestos, nonfibrous talc, fine titanium dioxide (TiO(2)), or glass beads for 8 or 24 h. Since crocidolite asbestos caused the greatest number of alterations in gene expression, multiplex analysis (Bio-Plex) of proteins released from LP9/TERT-1 cells exposed to crocidolite asbestos was also assessed to reveal if this approach might also be explored in future assays comparing various mineral types. To verify that LP9/TERT-1 cells were more sensitive than other cell types to asbestos, human ovarian epithelial cells (IOSE) were also utilized in microarray studies. Upon assessing changes in gene expression via microarrays, principal component analysis (PCA) of these data was used to identify patterns of differential gene expression. PCA of microarray data confirmed that LP9/TERT-1 cells were more responsive than IOSE cells to crocidolite asbestos or nonfibrous talc, and that crocidolite asbestos elicited greater responses in both cell types when compared to nonfibrous talc, TiO(2), or glass beads. Bio-Plex analysis demonstrated that asbestos caused an increase in interleukin-13 (IL-13), basic fibroblast growth factor (bFGF), granulocyte colony-stimulating factor (G-CSF), and vascular endothelial growth factor (VEGF). These responses were generally dose-dependent (bFGF and G-CSF only) and tumor necrosis factor (TNF)-alpha independent (except for G-CSF). Thus, microarray and Bio-Plex analyses are valuable in determining early molecular responses to fibers/particles and may directly contribute to understanding the etiology of diseases caused by them. The number and magnitude of changes in gene expression or "profiles" of secreted proteins may serve as valuable metrics for determining the potential pathogenicity of various mineral types. Hence, alterations in gene expression and cytokine/chemokine changes induced by crocidolite asbestos in LP9/TERT-1 cells may be indicative of its increased potential to cause mesothelioma in comparison to the other nonfibrous materials examined.

Selectively decreased expression of peroxiredoxins induced by silica in pulmonary epithelial cells

BACKGROUND/AIMS

Peroxiredoxin (Prx) belongs to a ubiquitous family of antioxidant enzymes that regulates many cellular processes through intracellular oxidative signal transduction pathways. Silica-induced lung damage involves reactive oxygen species (ROS) that trigger subsequent toxic effects and inflammatory responses in alveolar epithelial cells resulting in fibrosis. Therefore, we investigated the role of Prx in the development of lung oxidant injury caused by silicosis, and determined the implication of ROS in that process.

METHODS

Lung epithelial cell lines A549 and WI26 were treated with 1% silica for 0, 24, or 48 hours, following pretreatment of the A549 cells with N-acetyl-L-cysteine and diphenylene iodonium and no pretreatment of the WI26 cells. We transfected an HA-ubiquitin construct into the A549 cell line and then analyzed the cells via Western blotting and co-immunoprecipitation.

RESULTS

Silica treatment induced cell death in the A549 lung epithelial cell line and selectively degraded Prx I without impairing protein synthesis in the A549 cells, even when the ROS effect was blocked chemically by N-acetyl-L-cysteine. A co-immunoprecipitation study revealed that Prx I did not undergo ubiquitination.

CONCLUSIONS

Silica treatment induces a decrease of Prx I expression in lung epithelial cell lines regardless of the presence of ROS. The silica-induced degradation of Prx does not involve the ubiquitin-proteasomal pathway.

Biopersistence and potential adverse health impacts of fibrous nanomaterials: what have we learned from asbestos?

Human diseases associated with exposure to asbestos fibers include pleural fibrosis and plaques, pulmonary fibrosis (asbestosis), lung cancer, and diffuse malignant mesothelioma. The critical determinants of fiber bioactivity and toxicity include not only fiber dimensions, but also shape, surface reactivity, crystallinity, chemical composition, and presence of transition metals. Depending on their size and dimensions, inhaled fibers can penetrate the respiratory tract to the distal airways and into the alveolar spaces. Fibers can be cleared by several mechanisms, including the mucociliary escalator, engulfment, and removal by macrophages, or through splitting and chemical modification. Biopersistence of long asbestos fibers can lead to inflammation, granuloma formation, fibrosis, and cancer. Exposure to synthetic carbon nanomaterials, including carbon nanofibers and carbon nanotubes (CNTs), is considered a potential health hazard because of their physical similarities with asbestos fibers. Respiratory exposure to CNTs can produce an inflammatory response, diffuse interstitial fibrosis, and formation of fibrotic granulomas similar to that observed in asbestos-exposed animals and humans. Given the known cytotoxic and carcinogenic properties of asbestos fibers, toxicity of fibrous nanomaterials is a topic of intense study. The mechanisms of nanomaterial toxicity remain to be fully elucidated, but recent evidence suggests points of similarity with asbestos fibers, including a role for generation of reactive oxygen species, oxidative stress, and genotoxicity. Considering the rapid increase in production and use of fibrous nanomaterials, it is imperative to gain a thorough understanding of their biologic activity to avoid the human health catastrophe that has resulted from widespread use of asbestos fibers.

Serum growth factors in asbestosis patients

Various growth factors, including platelet-derived growth factor (PDGF) and transforming growth factor (TGF)-beta, have been implicated in the pathogenesis of asbestos-induced disease. PDGF and TGF-beta levels were determined by enzyme-linked immunosorbent assays in the banked serum samples of a cohort of workers with asbestosis, and the relationships of the growth factor levels to the subsequent development of cancer and to the radiographic severity and progression of asbestosis in the cohort were examined. Serum levels of PDGF and TGF-beta were found to be unrelated to the development of cancer, and serum levels of PDGF were found to be unrelated to the severity and progression of asbestosis. However, serum levels of TGF-beta were found to be statistically significantly related to disease severity (p = 0.01), increasing approximately 2.4-fold from ILO radiographic category 0 to category 3, and they were marginally related to disease progression (p = 0.07), in multivariate analysis controlling for other contributory factors including cumulative asbestos exposure. This suggests that serum TGF-beta may be a useful biomarker for asbestos-induced fibrotic disease.

Molecular Basis of Pulmonary Disease

Pulmonary pathology includes a large spectrum of both neoplastic and non-neoplastic diseases that affect the lung. Many of these are a result of the unusual relationship of the lung with the outside world. Every breath that a human takes brings the outside world into the body in the form of infectious agents, organic and inorganic particles, and noxious agents of all types. Although the lung has many defense mechanisms to protect itself from these insults, these are not infallible; therefore, lung pathology arises. Damage to the lung is particularly important given the role of the lung in the survival of the organism. Any impairment of lung function has widespread effects throughout the body, since all organs depend on the lungs for the oxygen they need. Pulmonary pathology catalogs the changes in the lung tissues and the mechanisms through which these occur. This chapter presents a review of lung pathology and the current state of knowledge about the pathogenesis of each disease. It suggests that a clear understanding of both morphology and mechanism is required for the development of new therapies and preventive measures.

Macrophage culture as a suitable paradigm for evaluation of synthetic vitreous fibers

The ultimate goal of toxicologic investigation of synthetic vitreous fibers (SVFs) is to provide essential input for the assessment of human risk to their exposure. Toxicity of mineral fibers is usually evaluated by testing biopersistence in rodent model. However, a cellular model would be much appreciated in order to reduce, refine, and replace animal models. Pulmonary disorders triggered by inhalation of occupational or environmental mineral particulates can be the endpoints of a chronic inflammatory process in which alveolar macrophages (AMs) play a crucial role. Depending on the type of SVF involved, phagocytosis of fiber leads to activation of macrophages, resulting in release of fiber components and potent mediators, such as reactive oxygen or nitrogen species and cytokines. As a matter of fact, macrophages should be the cells of choice since SVF toxicity is the consequence of fibers and alveolar macrophages interaction. Today, monocytes and macrophages culture are firmly established as a paradigm in toxicology when several endpoints are assayed in macrophages: (1) fiber durability, (2) fiber surface changes, (3) oxidative stress and genotoxicity in macrophage, and (4) macrophage cell viability and apoptosis. This article is a review of up-to-date knowledge of in vitro studies involving macrophages, and assesses endpoints of macrophage toxicity with an emphasis on (1) dissolution, (2) scanning electron microscopy analysis, (3) cytotoxicity, and (4) gene expression.

Renal, vascular and cardiac fibrosis in rats exposed to passive smoking and industrial dust fibre amosite

Passive smoking is an independent risk factor for cardiovascular diseases. Industrial fibrous dust, e.g. the asbestos group member, amosite, causes lung cancer and fibrosis. No data are available on renal involvement after inhalational exposure to these environmental pollutants or of their combination, or on cardiovascular and renal toxicity after exposure to amosite. Male Wistar rats were randomized into four groups (n= 6): control and amosite group received initially two intratracheal instillations of saline and amosite solution, respectively. Smoking group was subjected to standardized daily exposure to tobacco smoke for 2 hrs in a concentration resembling human passive smoking. Combined group was exposed to both amosite and cigarette smoke. All rats were killed after 6 months. Rats exposed to either amosite or passive smoking developed significant glomerulosclerosis and tubulointerstitial fibrosis. Combination of both exposures had additive effects. Histomorphological changes preceded the clinical manifestation of kidney damage. In both groups with single exposures, marked perivascular and interstitial cardiac fibrosis was detected. The additive effect in the heart was less pronounced than in the kidney, apparent particularly in changes of vascular structure. Advanced oxidation protein products, the plasma marker of the myeloperoxidase reaction in activated monocytes/macrophages, were increased in all exposed groups, whereas the inflammatory cytokines did not differ between the groups. In rats, passive smoking or amosite instillation leads to renal, vascular and cardiac fibrosis potentially mediated via increased myeloperoxidase reaction. Combination of both pollutants shows additive effects. Our data should be confirmed in subjects exposed to these environmental pollutants, in particular if combined.

Relationship between induced sputum cytology and inflammatory status with lung structural and functional abnormalities in asbestosis

BACKGROUND

Asbestosis is associated with lung cellular and immunological abnormalities. Induced sputum cytology and local and systemic markers of inflammation may be helpful to characterize disease status and progression in these patients.

METHODS

Thirty-nine ex-workers with asbestosis on high-resolution CT (HRCT) and 21 non-exposed controls were evaluated. Sputum cytology and IL-8 in serum and sputum were related to lung function impairment.

RESULTS

Subjects with asbestosis had reduced sputum cellularity but higher macrophage/neutrophil ratio and % macrophage as compared with controls. Sputum and serum IL-8 were also higher in patients with asbestosis (P < 0.05). In addition, evidence of lung architectural distorption on HRCT was associated with increased levels of serum IL-8. Interestingly, absolute macrophage number was negatively correlated with total lung capacity (r = -0.40; P = 0.04) and serum IL-8 to lung diffusing capacity (r = -0.45; P = 0.01).

CONCLUSIONS

Occupationally exposed subjects with asbestosis on HRCT have cytologic abnormalities in induced sputum and increased local and systemic pro-inflammatory status which are correlated to functional impairment.

The role of inflammation in the pathogenesis of idiopathic pulmonary fibrosis

The role of inflammation in idiopathic pulmonary fibrosis (IPF) is controversial. If inflammation were critical to the disease process, lung pathology would demonstrate an influx of inflammatory cells, and that the disease would respond to immunosuppression. Neither is true. The classic pathology does not display substantial inflammation, and no modulation of the immune system is effective as treatment. Recent data suggest that the pathophysiology of the disease is more a product of fibroblast dysfunction than of dysregulated inflammation. The role of inflammation in disease pathogenesis comes from pathology from atypical patients, biologic samples procured during exacerbations of the disease, and careful examination of biologic specimens from patients with stable disease. We suggest that inflammation is indeed a critical factor in IPF and propose five potential nontraditional mechanisms for the role of inflammation in the pathogenesis of IPF: the direct inflammatory hypothesis, the matrix hypothesis, the growth factor-receptor hypothesis, the plasticity hypothesis, and the vascular hypothesis. To address these, we review the literature exploring the differences in pathology, prognosis, and clinical course, as well as the role of cytokines, growth factors, and other mediators of inflammation, and last, the role of matrix and vascular supply in patients with IPF.

Translocation pathways for inhaled asbestos fibers

We discuss the translocation of inhaled asbestos fibers based on pulmonary and pleuro-pulmonary interstitial fluid dynamics. Fibers can pass the alveolar barrier and reach the lung interstitium via the paracellular route down a mass water flow due to combined osmotic (active Na+ absorption) and hydraulic (interstitial pressure is subatmospheric) pressure gradient. Fibers can be dragged from the lung interstitium by pulmonary lymph flow (primary translocation) wherefrom they can reach the blood stream and subsequently distribute to the whole body (secondary translocation). Primary translocation across the visceral pleura and towards pulmonary capillaries may also occur if the asbestos-induced lung inflammation increases pulmonary interstitial pressure so as to reverse the trans-mesothelial and trans-endothelial pressure gradients. Secondary translocation to the pleural space may occur via the physiological route of pleural fluid formation across the parietal pleura; fibers accumulation in parietal pleura stomata (black spots) reflects the role of parietal lymphatics in draining pleural fluid. Asbestos fibers are found in all organs of subjects either occupationally exposed or not exposed to asbestos. Fibers concentration correlates with specific conditions of interstitial fluid dynamics, in line with the notion that in all organs microvascular filtration occurs from capillaries to the extravascular spaces. Concentration is high in the kidney (reflecting high perfusion pressure and flow) and in the liver (reflecting high microvascular permeability) while it is relatively low in the brain (due to low permeability of blood-brain barrier). Ultrafine fibers (length < 5 mum, diameter < 0.25 mum) can travel larger distances due to low steric hindrance (in mesothelioma about 90% of fibers are ultrafine). Fibers translocation is a slow process developing over decades of life: it is aided by high biopersistence, by inflammation-induced increase in permeability, by low steric hindrance and by fibers motion pattern at low Reynolds numbers; it is hindered by fibrosis that increases interstitial flow resistances.

Laser capture microdissection reveals dose-response of gene expression in situ consequent to asbestos exposure

The genes that mediate fibroproliferative lung disease remain to be defined. Prior studies from our laboratory showed by in situ hybridization and immunohistochemistry that the genes coding for tumour necrosis factor alpha, transforming growth factor beta, the platelet-derived growth factor A and B isoforms, and alpha-1 pro-collagen are expressed in fibroproliferative lesions that develop quickly after asbestos inhalation. These five genes, along with matrix metalloproteinase 9, a collagenase found to be increased in several lung diseases, are known to control matrix production and cell proliferation in humans and animals. Here we show by laser capture microdissection that (i) The six genes are expressed at significantly higher levels in the asbestos-exposed mice when comparing the same anatomic regions 'captured' in unexposed mice. (ii) The bronchiolar-alveolar duct (BAD) junctions, where the greatest number of fibres initially deposit, were always significantly higher than the other anatomic regions for each gene. The first alveolar duct bifurcation (ADB) generally was higher than the second ADB, the ADBs were always significantly higher than the airway walls and pleura, and the airway walls and pleura were generally higher than the unexposed tissues. (iii) Animals exposed for 3 days always exhibited significantly higher levels of gene expression at the BAD junctions and ADBs than animals exposed for 2 days. To our knowledge, this is the first demonstration of a dose-response to a toxic particle in situ, and this response appears to be dependent on the number of fibres that deposits at the individual anatomic site.

Decreased asbestos-induced lung inflammation and fibrosis after radiation and bone marrow transplant

The effect of lung irradiation on subsequent inflammatory or fibrotic lung injuries remains poorly understood. We postulated that irradiation and bone marrow transplantation might impact the development and progression of lung remodeling resulting from asbestos inhalation. Our objective was to determine whether irradiation and bone marrow transplantation affected inflammation and fibrosis associated with inhaled asbestos exposure. Inflammation, cytokine production, and fibrosis were assessed in lungs of naïve and sex-mismatched chimeric mice exposed to asbestos for 3, 9, or 40 days. Potential engraftment of donor-derived cells in recipient lungs was examined by fluorescence in situ hybridization and immunohistochemistry. Compared with asbestos-exposed naïve (nonchimeric) mice, chimeric mice exposed to asbestos for 3, 9, or 40 days demonstrated significant abrogation of acute increases in asbestos-associated inflammatory mediators and fibrosis. Donor-derived cells trafficked to lung but did not significantly engraft as phenotypic lung cells. Irradiation and bone marrow transplantation alters inflammatory and fibrotic responses to asbestos, likely through modulation of soluble inflammatory mediators.

Differential in vitro cellular response induced by exposure to synthetic vitreous fibers (SVFs) and asbestos crocidolite fibers

In this study, we analyzed the effects of synthetic vitreous fibers (SVFs) on a mesothelial (MeT5A) and a fibroblast cell line (NIH3T3), compared to those exerted by crocidolite asbestos fibers. SVFs (glass wool, rock wools) do not induce significant changes in cell mortality, whereas crocidolite asbestos fibers caused a dose-dependent cytotoxicity. We investigated the correlation between the fiber-induced cytotoxicity and the extent and type of interaction of the fibers with the cell surface, and we observed that SVFs, unlike crocidolite asbestos fibers, establish few and weak interactions. Moreover, after internalization, crocidolite asbestos fibers are often found free in the cytoplasm, whereas glass wool fibers are mainly localized inside cytoplasmic vacuoles. After treatments, we also detected signs of oxidative stress, revealed by an increased reactive oxygen species (ROS) production and by an induction of superoxide dismutase (SOD) activity. The lipoperoxidative damage was characterized by a decrease in polyunsaturated fatty acids (PUFA), an increase in the content of thiobarbituric reactive species (TBARS) and a consumption of vitamin E, as a lipophilic antioxidant. Furthermore, we investigated the effect of fiber exposure on cell proliferation. and it was found that, unlike crocidolite asbestos fibers, SVFs did not induce a significant increase in DNA synthesis.

Pleural fibrosis

Pleural fibrosis can result from a variety of inflammatory processes. The response of the pleural mesothelial cell to injury and the ability to maintain its integrity are crucial in determining whether normal healing or pleural fibrosis occurs. The pleural mesothelial cell, various cytokines, and disordered fibrin turnover are involved in the pathogenesis of pleural fibrosis. The roles of these mediators in producing pleural fibrosis are examined. This article reviews the most common clinical conditions associated with the development of pleural fibrosis. Fibrothorax and trapped lung are two unique and uncommon consequences of pleural fibrosis. The management of pleural fibrosis, including fibrothorax and trapped lung, is discussed.

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

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

Genetic Predisposition to Fiber Carcinogenesis Causes a Mesothelioma Epidemic in Turkey

Malignant mesothelioma in the western world is often associated with asbestos exposure. It is a relatively rare cancer that causes approximately 2,500 deaths yearly in the United States and 1,000 deaths yearly in the United Kingdom. In contrast, among people born in the Cappadocian (Turkey) villages of Tuzkoy, Karain, and "Old" Sarihidir, approximately 50% of deaths are caused by malignant mesothelioma. This epidemic has been attributed to erionite exposure, a type of fibrous zeolite mineral commonly found in this area of Turkey. In these three villages, malignant mesothelioma occurs in certain houses but not in others. The hypothesis was that a unique and more carcinogenic erionite was present in certain houses and caused malignant mesothelioma. We determined the X-ray diffraction pattern and the crystal structure of erionite from malignant mesothelioma villages and compared the results with the erionite samples from nearby non-malignant mesothelioma villages and from the United States. We found the same type of erionite in Cappadocian villages, with or without a malignant mesothelioma epidemic, in households with high or no incidence of malignant mesothelioma and in the United States. Pedigree studies of the three malignant mesothelioma villages showed that malignant mesothelioma was prevalent in certain families but not in others. When high-risk malignant mesothelioma family members married into families with no history of it, malignant mesothelioma appeared in the descendants. Genetically predisposed family members born and raised outside the malignant mesothelioma villages did not seem to develop malignant mesothelioma. In summary, pedigree and mineralogical studies indicate that the malignant mesothelioma epidemic is caused by erionite exposure in genetically predisposed individuals. This is the first time that genetics is shown to influence mineral fiber carcinogenesis.