Recent progress and perspectives on the mechanisms underlying Asbestos toxicity

Ecotoxicological effects of short-term exposure to elongated tunnel particles from two road construction sites on juvenile Atlantic salmon (Salmo salar)

Tunnelling through rock to facilitate transportation and logistics is common worldwide. However, the negative impacts of discharge emissions from tunnel construction on aquatic environments are not well understood. This study aimed to increase knowledge about the ecotoxicological effects of particle discharge from two tunnel construction sites (Rafoss and Verket) in Norway on juvenile Atlantic salmon (Salmo salar). Fish were exposed to environmentally relevant (100 mg/L) and high concentrations (Rafoss: 2800 mg/L, Verket: 5000 mg/L) for 192 h. Particles from both sites (47-51 % < 10 μm in diameter), primarily granite-gneiss bedrock and slightly more elongated than naturally eroded particles, created distinct water environments due to geological and chemical differences. This is the first peer-reviewed study to utilize μCT for quantification of particle retention in gills and it allowed identifying concentration-dependent retention, with higher retention for Verket particles, likely due to water chemistry differences. Despite high retention, no histological changes were observed. Mortality occurred at ≥3500 mg/L Verket particles after 48 and 24 h, plausibly due to suffocation from gill clogging. The LC50 for Verket particles was 3137 mg/L. Suffocation likely caused a drop in plasma Cl levels due to elevated pCO2. Elements with high particulate fractions accumulated in gills and stomach contents in a concentration-dependent manner for both particle types, and in livers at ≥3500 mg/L. No acute or sublethal effects, including metal toxicity, were observed at concentrations up to 2000 mg/L Verket and 2800 mg/L Rafoss particles for 192 h. These results suggest that common benchmarks of 50-400 mg/L in emission permits do not cause acute or sublethal effects in juvenile Atlantic salmon during short-term exposures.

The empirical metric of mesothelial carcinogenicity for carbon nanotubes and elongate mineral particles

INTRODUCTION

Carcinogenic potential of elongate particles depends on many characteristics, with dimensional parameters playing an important role at all stages of disease origination and progression. It is important to develop quantitative metrics of mesothelial carcinogenicity for particles in order to predict their behavior within biological systems. It would be especially valuable if such metrics could be developed for both carbon nanotubes (CNTs) and elongate mineral particles (EMPs) to demonstrate similarities and differences in the estimations of mesothelioma risk.

METHODS

The database is organized with dimensional characteristics of EMPs, containing 570,950 records for 246 asbestiform, non-asbestiform, and mixed datasets. A database on carbon nanotubes (CNTs) with various toxicological outcomes of animal experiments, including mesothelioma, was also created. Mathematical modeling was used to determine the best metric of mesotheliomagenicity that would work for CNTs and EMPs.

RESULTS

The dimensional coefficient of carcinogenicity (DCC) was introduced with the formula DCC = 1-exp(-AxSA/(BxWidth3+C)), where SA - surface area of the elongate particle, Width - particle width, A, B, C - coefficients. It was demonstrated that DCC can efficiently determine mesotheliomagenic varieties of CNTs and EMPs, with a threshold for carcinogenic potential of 0.05 with A = 0.11, B = 1000, C = 1.

DISCUSSION

The new quantitative metric of carcinogenicity can be used for the purposes of mineralogical evaluation and toxicological analysis. It was confirmed that DCC-based models predict negligible mesothelioma potency for non-asbestiform amphiboles.

Critical values for dimensional parameters of mesotheliomagenic mineral fibers: evidence from the dimensions and rigidity of MWCNT

MWCNT (multi-walled carbon nanotubes) used in 72 animal instillation or inhalation studies were classified by average length, average width, Young's modulus, Rigidity Index (RI), and potency for mesothelioma in animals. The RI is based on the Euler buckling theory. MWCNT that induce mesothelioma have average lengths >2 µm and widths >37 nm, and average RI > 0.05 (µm2 x GPa x 104). Many noncarcinogenic MWCNT materials have RI < 0.05 and lack biological rigidity. In comparison, Elongate Mineral Particle (EMP) populations with one exception have RI > 0.05. Mineral particles likely to have RI < 0.05 include chrysotile fibrils with lengths >5 μm, amosite and crocidolite fibers with widths <60 nm, and sheet silicate fibers with widths <200 nm. The product of percent EMPA, average RI, and biosolubility among silicates correlates with known mesothelioma potency. The derived models reproduce published values of RM with high statistical significance (P < 0.05). Average RI, length, and width are critical parameters for mesotheliomagenicity for both MWCNT and EMPA mineral fiber.

Evaluation of the genotoxic and transformation potential induced by asbestos compared to cleavage fragments

The World Health Organization has confirmed that asbestos fibres are carcinogenic, claiming that asbestos-related diseases should be eradicated worldwide. Actinolite, amosite, anthophyllite, chrysotile, crocidolite, and tremolite are regulated asbestiform mineral phases. However, in nature, asbestos minerals occur either in a fibrous and asbestiform (original morphology characterized by high length-to-width ratio and provided of high tensile strength and flexibility) or fibrous but not asbestiform appearance. This study used human epithelial cancer cells (A549) and a mouse fibroblast cell line (Balb/c 3T3) to compare the genotoxic and carcinogenic effects of a sample of amphibole asbestos with samples of fibrous not asbestiform named cleavage fragments (CV) obtained by grinding non-asbestiform amphiboles. The results showed that exposure of alveolar lung cells to asbestos and elongated mineral particles, in the habit of cleavage fragments (CF) derived from the grinding of non-asbestiform amphiboles and serpentines, causes cytotoxic effects, oxidative stress and genotoxic damage. Moreover, CF obtained from an actinolite schist induces a transformation effect in the Balb/c 3T3 model. Together, these findings highlight the importance of considering CF as a potential threat to human health since it can cause genotoxic damage by triggering cellular transformation processes that overlap with the mechanisms involved in the carcinogenesis processes of asbestos.

The role of pathologists in the diagnosis of occupational lung diseases: an expert opinion of the European Society of Pathology Pulmonary Pathology Working Group

Occupational lung/thoracic diseases are a major global public health issue. They comprise a diverse spectrum of health conditions with complex pathology, most of which arise following chronic heavy workplace exposures to various mineral dusts, metal fumes, or following inhaled organic particulate reactions. Many occupational lung diseases could become irreversible; thus accurate diagnosis is mandatory to minimize dust exposure and consequently reduce damage to the respiratory system. Lung biopsy is usually required when exposure history is inconsistent with imaging, in case of unusual or new exposures, in case of unexpected malignancy, and in cases in which there are claims for personal injury and legal compensation. In this paper, we provide an overview of the most frequent occupational lung diseases with a focus on pathological diagnosis. This is a paper that summarizes the expert opinion from a group of European pathologists, together with contributions from other specialists who are crucial for the diagnosis and management of these diseases. Indeed, tight collaboration of all specialists involved in the workup is mandatory as many occupational lung diseases are misdiagnosed or go unrecognized. This document provides a guide for pathologists in practice to facilitate the accurate diagnosis of occupational lung disease. The review article reports relevant topics discussed during an educational course held by expert pathologists, active members of the Pulmonary Pathology Working Group of the European Society of Pathology. The course was endorsed by the University of Padova as a "winter school" (selected project in the call for "Shaping a World-class University" 2022).

Amphibole asbestos as an environmental trigger for systemic autoimmune diseases

A growing body of evidence supports an association between systemic autoimmune disease and exposure to amphibole asbestos, a form of asbestos typically with straight, stiff, needle-like fibers that are easily inhaled. While the bulk of this evidence comes from the population exposed occupationally and environmentally to Libby Amphibole (LA) due to the mining of contaminated vermiculite in Montana, studies from Italy and Australia are broadening the evidence to other sites of amphibole exposures. What these investigations have done, that most historical studies have not, is to evaluate amphibole asbestos separately from chrysotile, the most common commercial asbestos in the United States. Here we review the current and historical evidence summarizing amphibole asbestos exposure as a risk factor for autoimmune disease. In both mice and humans, amphibole asbestos, but not chrysotile, drives production of both antinuclear autoantibodies (ANA) associated with lupus-like pathologies and pathogenic autoantibodies against mesothelial cells that appear to contribute to a severe and progressive pleural fibrosis. A growing public health concern has emerged with revelations that a) unregulated asbestos minerals can be just as pathogenic as commercial (regulated) asbestos, and b) bedrock and soil occurrences of asbestos are far more widespread than previously thought. While occupational exposures may be decreasing, environmental exposures are on the rise for many reasons, including those due to the creation of windborne asbestos-containing dusts from urban development and climate change, making this topic an urgent challenge for public and heath provider education, health screening and environmental regulations.

The Additional Burden of Earthquakes: Asbestos Risks Rising in Turkey

Cite this article as: Yavuz CI. The additional burden of earthquakes: Asbestos risks rising in Türkiye. Thorac Res Pract. 2024;25(3):100-101.

Club Cells-A Guardian against Occupational Hazards

Club cells have a distinct role in the epithelial repair and defense mechanisms of the lung. After exposure to environmental pollutants, during chronic exposure, the secretion of club cells secretory protein (CCSP) decreases. Exposure to occupational hazards certainly has a role in a large number of interstitial lung diseases. According to the American Thoracic Society and the European Respiratory Society, around 40% of the all interstitial lung disease is attributed to occupational hazards. Some of them are very well characterized (pneumoconiosis, hypersensitivity pneumonitis), whereas others are consequences of acute exposure (e.g., paraquat) or persistent exposure (e.g., isocyanate). The category of vapors, gases, dusts, and fumes (VGDF) has been proven to produce subclinical modifications. The inflammation and altered repair process resulting from the exposure to occupational respiratory hazards create vicious loops of cooperation between epithelial cells, mesenchymal cells, innate defense mechanisms, and immune cells. The secretions of club cells modulate the communication between macrophages, epithelial cells, and fibroblasts mitigating the inflammation and/or reducing the fibrotic process. In this review, we describe the mechanisms by which club cells contribute to the development of interstitial lung diseases and the potential role for club cells as biomarkers for occupational-related fibrosis.

Effects of SETD2 on telomere length and malignant transformation property of Met-5A after one-month crocidolite exposure

Crocidolite is a carcinogen contributing to the pathogenesis of malignant mesothelioma. This study aimed to characterize the possible telomere-related events mediating the malignant transformation of mesothelial cells with and without SETD2 under crocidolite exposure. The crocidolite concentration resulting in 90% viable SETD2 knockout Met-5A (Met-5ASETD2-KO) and Met-5A were estimated to be 0.71 μg/cm2 and 1.8 μg/cm2, respectively, during 72 h of exposure, which was further employed in chronical crocidolite exposure during a 72 h exposure interval per time up to 1 month. Chronical crocidolite-exposed Met-5ASETD2-KO (chronical Cro-Met-5ASETD2-KO) had higher colony formation and increased telomerase reverse transcriptase (TERT) protein levels than chronical crocidolite-exposed Met-5A (chronical Cro-Met-5A) and Met-5ASETD2-KO. Chronical Cro-Met-5ASETD2-KO had longer telomere length (TL) than chronical Cro-Met-5A, although there were no changes in TL for either chronical Cro-Met-5A or chronical Cro-Met-5ASETD2-KO compared with their corresponding cells without crocidolite exposure. BIBR 1532, an inhibitor targeting TERT, partially reduced colony formation and TL for chronical Cro-Met-5ASETD2-KO, while BIBR 1532 reduced TL but had no effect on colony formation for chronical Cro-Met-5A. Therefore, SETD2 deficient mesothelial cells are susceptible to malignant transformation during chronical crocidolite exposure, and TERT-dependent TL modification likely partially drives SETD2 loss-mediated early onset of mesothelial malignant transformation.

Distinct Pro-Inflammatory Mechanisms Elicited by Short and Long Amosite Asbestos Fibers in Macrophages

While exposure to long amphibolic asbestos fibers (L > 10 µm) results in the development of severe diseases including inflammation, fibrosis, and mesothelioma, the pathogenic activity associated with short fibers (L < 5 µm) is less clear. By exposing murine macrophages to short (SFA) or long (LFA) fibers of amosite asbestos different in size and surface chemistry, we observed that SFA internalization resulted in pyroptotic-related immunogenic cell death (ICD) characterized by the release of the pro-inflammatory damage signal (DAMP) IL-1α after inflammasome activation and gasdermin D (GSDMD)-pore formation. In contrast, macrophage responses to non-internalizable LFA were associated with tumor necrosis factor alpha (TNF-α) release, caspase-3 and -7 activation, and apoptosis. SFA effects exclusively resulted from Toll-like receptor 4 (TLR4), a pattern-recognition receptor (PRR) recognized for its ability to sense particles, while the response to LFA was elicited by a multifactorial ignition system involving the macrophage receptor with collagenous structure (SR-A6 or MARCO), reactive oxygen species (ROS) cascade, and TLR4. Our findings indicate that asbestos fiber size and surface features play major roles in modulating ICD and inflammatory pathways. They also suggest that SFA are biologically reactive in vitro and, therefore, their inflammatory and toxic effects in vivo should not be underestimated.

Characteristics of transcription profile, adhesion and migration of SETD2-loss Met-5A mesothelial cells exposed with crocidolite

Asbestos is a fibrous silicate mineral exhibiting biopersistence and carcinogenic properties and contributes to mesothelioma. Despite the concept of gene-environmental interaction in pathogenesis of mesothelioma, the possible pathophysiological changes of mesothelial cells simultaneously with SET domain containing 2 (SETD2) loss and asbestos exposure remains obscure. Herein, CRISPR/Cas9-mediated SETD2 knockout Met-5A mesothelial cells (Met-5ASETD2-KO ) were established and exposed with crocidolite, an amphibole asbestos. Cell viability of Met-5ASETD2-KO appeared to dramatically decrease with ≥2.5 μg/cm2 crocidolite exposure as compared with Met-5A, although no cytotoxicity and apoptosis changes of Met-5ASETD2-KO and Met-5A was evident with 1.25 μg/cm2 crocidolite exposure for 48 h. RNA sequencing uncovered top 50 differentially expressed genes (DEGs) between 1.25 μg/cm2 crocidolite exposed Met-5ASETD2-KO (Cro-Met-5ASETD2-KO ) and 1.25 μg/cm2 crocidolite exposed Met-5A (Cro-Met-5A), and ITGA4, THBS2, MYL7, RAC2, CADM1, and CLDN11 appeared to be the primary DEGs involved with adhesion in gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Cro-Met-5ASETD2-KO had strong migration but mild adhesion behavior as compared with Cro-Met-5A. Additionally, crocidolite tended to increase migration of Met-5ASETD2-KO but inhibited migration of Met-5A when compared with their corresponding cells without crocidolite exposure, although no further adhesion property changes was evident for both cells in response to crocidolite. Therefore, crocidolite may affect adhesion-related gene expression and modify adhesion and migration behavior for SETD2-depleted Met-5A, which could provide preliminary insight regarding the potential role of SETD2 in the cell behavior of asbestos-related malignant mesothelial cell.

APDB: a database on air pollutant characterization and similarity prediction

The World Health Organization estimates that 9 out of 10 people worldwide breathe air containing high levels of pollutants. Long-term and chronic exposure to high concentrations of air pollutants is associated with deleterious effects on vital organs, including increased inflammation in the lungs, oxidative stress in the heart and disruption of the blood-brain barrier. For this reason, in an effort to find an association between exposure to pollutants and the toxicological effects observable on human health, an online resource collecting and characterizing in detail pollutant molecules could be helpful to investigate their properties and mechanisms of action. We developed a database, APDB, collecting air-pollutant-related data from different online resources, in particular, molecules from the US Environmental Protection Agency, their associated targets and bioassays found in the PubChem chemical repository and their computed molecular descriptors and quantum mechanics properties. A web interface allows (i) to browse data by category, (ii) to navigate the database by querying molecules and targets and (iii) to visualize and download molecule and target structures as well as computed descriptors and similarities. The desired data can be freely exported in textual/tabular format and the whole database in SQL format. Database URL http://apdb.di.univr.it.

Synthesis of Ni-Doped Tremolite Fibers to Help Clarify the Aetiology of the Cytotoxic Outcome of Asbestos

Asbestos fibers act as complex crystal-chemical reservoirs susceptible of releasing potentially toxic elements (such as ions impurities) into the lung cellular environment during permanency and dissolution. To comprehend the exact pathological mechanisms that are triggered upon inhalation of asbestos fibers, in vitro studies on possible interactions between the mineral and the biological system have been carried out mostly by using natural asbestos. However, this latter comprises intrinsic impurities such as Fe²⁺/Fe³⁺ and Ni²⁺ ions, and other eventual traces of metallic pathogens. Furthermore, often, natural asbestos is characterized by the co-presence of several mineral phases, fiber dimensions of which are randomly distributed in width and in length. For these reasons, it is albeit challenging to precisely identify toxicity factors and to define the accurate role of each factor in the overall pathogenesis of asbestos. In this regard, the availability of synthetic asbestos fibers with accurate chemical composition and specific dimensions for in vitro screening tests would represent the perfect tool to correlate asbestos toxicity to its chemico-physical features. Herein, to palliate such drawbacks of natural asbestos, well-defined Ni-doped tremolite fibers were chemically synthesized in order to offer biologists adequate samples for testing the specific role of Ni²⁺ in asbestos toxicity. The experimental conditions (temperature, pressure, reaction time and water amount) were optimized to produce batches of asbestos fibers of the tremolite phase, with uniformly distributed shape and dimensions and a controlled content of Ni²⁺ metal ions.

Benefits and Challenges of Inhibiting EZH2 in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive thoracic cancer that is mainly associated with prior exposure to asbestos fibers. Despite being a rare cancer, its global rate is increasing and the prognosis remains extremely poor. Over the last two decades, despite the constant research of new therapeutic options, the combination chemotherapy with cisplatin and pemetrexed has remained the only first-line therapy for MPM. The recent approval of immune checkpoint blockade (ICB)-based immunotherapy has opened new promising avenues of research. However, MPM is still a fatal cancer with no effective treatments. Enhancer of zeste homolog 2 (EZH2) is a histone methyl transferase that exerts pro-oncogenic and immunomodulatory activities in a variety of tumors. Accordingly, a growing number of studies indicate that EZH2 is also an oncogenic driver in MPM, but its effects on tumor microenvironments are still largely unexplored. This review describes the state-of-the-art of EZH2 in MPM biology and discusses its potential use both as a diagnostic and therapeutic target. We highlight current gaps of knowledge, the filling of which will likely favor the entry of EZH2 inhibitors within the treatment options for MPM patients.

Particle Debris Generated from Passenger Tires Induces Morphological and Gene Expression Alterations in the Macrophages Cell Line RAW 264.7

Air pollution in the urban environment is a topical subject. Aero-suspended particles can cause respiratory diseases in humans, ranging from inflammation to asthma and cancer. One of the components that is most prevalent in particulate matter (PM) in urban areas is the set of tire microparticles (1-20 μm) and nanoparticles (<1 μm) that are formed due to the friction of wheels with asphalt and are increased in slow-moving areas that involve a lot of braking actions. In this work, we studied the effect that microparticles generated from passenger tires (PTWP, passenger tire wear particles) have in vitro on murine macrophages cells RAW 264.7 at two concentrations of 25 and 100 μg/mL, for 24 and 48 h. In addition to the chemical characterization of the material and morphological characterization of the treated cells by transmission electron microscopy, gene expression analysis with RT-PCR and active protein analysis with Western blotting were performed. Growth curves were obtained, and the genotoxic effect was evaluated with a comet assay. The results indicate that initially, an induction of the apoptotic process is observable, but this is subsequently reversed by Bcl2. No genotoxic damage is present, but mild cellular abnormalities were observed in the treated cells.

A rapid review and meta-regression analyses of the toxicological impacts of microplastic exposure in human cells

Humans are exposed to microplastics (MPs) daily via ingestion and inhalation. It is not known whether this results in adverse health effects and, if so, at what levels of exposure. Without epidemiological studies, human cell in vitro MP toxicological studies provide an alternative approach to this question. This review systematically synthesised all evidence and estimated thresholds of dose-response relationships. MEDLINE and Web of Science were searched from inception to March 2021 and study quality was rated using a novel risk of bias assessment tool. Seventeen studies were included in the rapid review and eight in the meta-regression. Four biological endpoints displayed MP-associated effects: cytotoxicity, immune response, oxidative stress, barrier attributes, and one did not (genotoxicity). Irregular shape was found to be the only MP characteristic predicting cell death, along with the duration of exposure and MP concentration (μg/mL). Cells showed varying cytotoxic sensitivity to MPs, with Caco-2 cells (human adenocarcinoma cell line) being the most susceptible. Minimum, environmentally-relevant, concentrations of 10 μg/mL (5-200 µm), had an adverse effect on cell viability, and 20 μg/mL (0.4 µm) on cytokine release. This work is the first to quantify thresholds of MPs effects on human cells in the context of risk assessment.