A mechanistic review of silica-induced inhalation toxicity

FAP expression dynamics and role in silicosis: Insights from epidemiological and experimental models

Prolonged exposure to free silica leads to the development of silicosis, wherein activated fibroblasts play a pivotal role in its pathogenesis and progression. Fibroblast Activation Protein (FAP), as a biomarker for activated fibroblasts, its expression pattern and role in key aspects of silicosis pathogenesis remain unclear. This study elucidated the expression pattern and function of FAP through population-based epidemiological investigations, establishment of mouse models of silicosis, and in vitro cellular models. Results indicated a significant elevation of FAP in plasma from silicosis patients and lung tissues from mouse models of silicosis. In the cellular model, we observed a sharp increase in FAP expression early in the differentiation process, which remained high expression. Inhibition of FAP suppressed fibroblast differentiation, while overexpression of FAP produced the opposite effect. Moreover, fibroblast-derived FAP can alter the phenotype and function of neighboring macrophages. In summary, we revealed a high expression pattern of FAP in silicosis and its potential mechanistic role in fibrosis, suggesting FAP as a potential therapeutic target for silicosis.

Aluminium bioaccumulation in colon cancer, impinging on epithelial-mesenchymal-transition and cell death

We investigated the presence of aluminium (Al) in human colon cancer samples and its potential association with biological processes involved in cancer progression, such as epithelial to mesenchymal transition (EMT) and cell death. 25 consecutive colon samples were collected from patients undergoing colonic resection. Both neoplastic and normal mucosa were collected from each patient and subjected to histological, ultrastructural and immunohistochemical analyses. Moreover, colon samples from two Al-positive patients underwent multi-omic analyses, including whole genome sequencing and RNA sequencing (RNAseq). Morin staining, used to identify in situ aluminium bioaccumulation, showed the presence of Al in tumor areas of 24 % of patients. Transmission electron microscopy and energy-dispersive X-ray microanalysis confirmed the presence of Al specifically in intracytoplasmic electrondense nanodeposits adjacent to mitochondria of colon cancer cells. Immunohistochemical analyses for vimentin and nuclear β-catenin were performed to highlight the occurrence of the EMT phenomenon in association to Al bioaccumulation. Al-positive samples showed a significant increase in both the number of vimentin-positive and nuclear β-catenin-positive cancer cells compared to Al-negative samples. Moreover, Al-positive samples exhibited a significant decrease in the number of apoptotic cells, as well as the expression of the anti-apoptotic molecule BCL-2. Multi-omic analyses revealed a higher tumor mutational burden (TMB) in Al-positive colon cancers (n = 2) compared to a control cohort (n = 100). Additionally, somatic mutations in genes associated with EMT (GATA3) and apoptosis (TP53) were observed in Al-positive colon cancers. In conclusion, this study provides the first evidence of Al bioaccumulation in colon cancer and its potential role in modulating molecular pathways involved in cancer progression, such as EMT and apoptosis. Understanding the molecular mechanisms underlying Al toxicity might contribute to improve strategies for prevention, early detection, and targeted therapies for the management of colon cancer patients.

The role of mitochondrial dysfunction in macrophages on SiO2 -induced pulmonary fibrosis: A review

Several epidemiologic and toxicological studies have widely regarded that mitochondrial dysfunction is a popular molecular event in the process of silicosis from different perspectives, but the details have not been systematically summarized yet. Thus, it is necessary to investigate how silica dust leads to pulmonary fibrosis by damaging the mitochondria of macrophages. In this review, we first introduce the molecular mechanisms that silica dust induce mitochondrial morphological and functional abnormalities and then introduce the main molecular mechanisms that silica-damaged mitochondria induce pulmonary fibrosis. Finally, we conclude that the mitochondrial abnormalities of alveolar macrophages caused by silica dust are involved deeply in the pathogenesis of silicosis through these two sequential mechanisms. Therefore, reducing the silica-damaged mitochondria will prevent the potential occurrence and fatality of the disease in the future.

Environmental Causes of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF), the most common and severe of the idiopathic interstitial pneumonias, is a chronic and relentlessly progressive disease, which occurs mostly in middle-aged and elderly males. Although IPF is by definition "idiopathic", multiple factors have been reported to increase disease risk, aging being the most prominent one. Several occupational and environmental exposures, including metal dust, wood dust and air pollution, as well as various lifestyle variables, including smoking and diet, have also been associated with an increased risk of IPF, probably through interaction with genetic factors. Many of the predisposing factors appear to act also as trigger for acute exacerbations of the disease, which herald a poor prognosis. The more recent literature on inhalation injuries has focused on the first responders in the World Trade Center attacks and military exposure. In this review, we present an overview of the environmental and occupational causes of IPF and its pathogenesis. While our list is not comprehensive, we have selected specific exposures to highlight based on their overall disease burden.

Emerging trends in silicosis research: a scientometric review

Silicosis is a global disease whose prevention efforts cannot be ignored today. Although numerous silicosis-related data have been published recently, emphasizing the characteristics and nature of silicosis, a summary of the developmental laws of research is lacking, especially in the visual analysis of the literature. We aim to address this issue through a scientometric review. The Web of Science Core Collection and the All Databases were searched with "silicosis" as the topic, excluding unrelated publications, and obtained data from 9802 and 1613 publications, respectively. The data was then analyzed using the Web of Science's online scientometric analysis function and CiteSpace's visual analysis functionality, including publication volume analysis, co-occurrence analysis, co-citation analysis, cluster analysis, and explosive detection. The results identify the "respiratory system" as the most influential area over a century. Furthermore, the publication's number was correlated with the gross domestic product. We ranked countries and institutions based on the frequency of publications and discovered that Europe, the USA, and China are the leading regions for silicosis research, with the USA and Europe having a stronger influence. Many reports related to artificial stone and denim jean production have been studied through citation analysis, indicating new epidemic trends in silicosis. Besides, silicosis-related diseases and the pathogenesis of silicosis were the research hotspots of silicosis through co-occurrence keyword analysis and outbreak detection. Furthermore, related diseases include coal workers' pneumoconiosis and tuberculosis, while the mechanism of silicosis includes studies on inflammation and fibrosis, oxidative stress, alveolar macrophages, apoptosis, and pathways.

Animal models of silicosis: fishing for new therapeutic targets and treatments

Silicosis as an occupational lung disease has been present in our lives for centuries. Research studies have already developed and implemented many animal models to study the pathogenesis and molecular basis of the disease and enabled the search for treatments. As all experimental animal models used to date have their advantages and disadvantages, there is a continuous search for a better model, which will not only accelerate basic research, but also contribute to clinical aspects and drug development. We review here, for the first time, the main animal models developed to date to study silicosis and the unique advantages of the zebrafish model that make it an optimal complement to other models. Among the main advantages of zebrafish for modelling human diseases are its ease of husbandry, low maintenance cost, external fertilisation and development, its transparency from early life, and its amenability to chemical and genetic screening. We discuss the use of zebrafish as a model of silicosis, its similarities to other animal models and the characteristics of patients at molecular and clinical levels, and show the current state of the art of inflammatory and fibrotic zebrafish models that could be used in silicosis research.

Barium sulphate microparticles are taken up by three different cell types: HeLa, THP-1, and hMSC

Cytotoxicity and cellular uptake of spherical barium sulphate microparticles (diameter 1 µm) were studied with three different cell lines, i.e. THP-1 cells (monocytes; model for a phagocytosing cell line), HeLa cells (epithelial cells; model for a non-phagocytosing cell line), and human mesenchymal stem cells (hMSCs; model for non-phagocytosing primary cells). Barium sulphate is a chemically and biologically inert solid which allows to distinguish two different processes, e.g. the particle uptake and potential adverse biological reactions. Barium sulphate microparticles were surface-coated by carboxymethylcellulose (CMC) which gave the particles a negative charge. Fluorescence was added by conjugating 6-aminofluorescein to CMC. The cytotoxicity of these microparticles was studied by the MTT test and a live/dead assay. The uptake was visualized by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The particle uptake mechanism was quantified by flow cytometry with different endocytosis inhibitors in THP-1 and HeLa cells. The microparticles were easily taken up by all cell types, mostly by phagocytosis and micropinocytosis, within a few hours. STATEMENT OF SIGNIFICANCE: The interaction of particles and cells is of primary importance in nanomedicine, drug delivery, and nanotoxicology. It is commonly assumed that cells take up only nanoparticles unless they are able to phagocytosis. Here, we demonstrate with chemically and biologically inert microparticles of barium sulphate that even non-phagocytosing cells like HeLa and hMSCs take up microparticles to a considerable degree. This has considerable implication in biomaterials science, e.g. in case of abrasive debris and particulate degradation products from implants like endoprostheses.

The temporal characteristics of the disruption of gut microbiota, serum metabolome, and cytokines by silica exposure in wistar rats

Silicosis is one of the most frequent, rapidly developing, and lethal types of pneumoconiosis. However, our understanding of the underlying mechanisms of its pathogenesis and progress remains unclear. We investigated the fundamental processes of silicosis incidence and progression using a combination of lung function testing, histopathology, 16 S rRNA, untargeted metabolomics, and cytokine chips at different exposure times (4 or 8 weeks). The results show that silica exposure damages lung tissue reduces lung function, and increases with time. Cytokines with time-specific properties were found in lung lavage fluid: IFN-γ (4 weeks; P＜0.05), TNF-α, M-CSF, GM-CSF (8 weeks; P＜0.01). In addition, silica exposure for different periods interferes to varying degrees with the metabolism of lipids. The composition of the intestinal microbiota changed with increasing exposure time and there were time-specific: Allobaculum, Turicibacter、Jeotgalicoccu、Coprococcus 1 (4 weeks; P＜0.05), Ruminococcaceae NK4A214 group、Ruminiclostridium 5 (8 weeks; P＜0.05). We found strong associations between cytokines, gut microbiota changes, and metabolic disturbances at different exposure times. These results suggest that time-specific changes in crosstalk among cytokines, the gut microbiota, and metabolites may be a potential mechanism for silica-induced lung injury.

Nearly free silanols drive the interaction of crystalline silica polymorphs with membranes: Implications for mineral toxicity

Crystalline silica (CS) is a well-known hazardous material that causes severe diseases including silicosis, lung cancer, and autoimmune diseases. However, the hazard associated to crystalline silica is extremely variable and depends on some specific characteristics, including crystal structure and surface chemistry. The crystalline silica polymorphs share the SiO₂ stoichiometry and differentiate for crystal structure. The different crystal lattices in turn expose differently ordered hydroxyl groups at the crystal surface, i.e., the silanols. The nearly free silanols (NFS), a specific population of weakly interacting silanols, have been recently advanced as the key surface feature that governs recognition mechanisms between quartz and cell membrane, initiating toxicity. We showed here that the nearly free silanols occur on the other crystalline silica polymorphs and take part in the molecular interactions with biomembranes. A set of crystalline silica polymorphs, including quartz, cristobalite, tridymite, coesite, and stishovite, was physico-chemically characterized and the membranolytic activity was assessed using red blood cells as model membranes. Infrared spectroscopy in highly controlled conditions was used to profile the surface silanol topochemistry and the occurrence of surface nearly free silanols on crystalline silica polymorphs. All crystalline silica polymorphs, but stishovite were membranolytic. Notably, pristine stishovite did not exhibited surface nearly free silanols. The topochemistry of surface silanols was modulated by thermal treatments, and we showed that the occurrence of nearly free silanols paralleled the membranolytic activity for the crystalline silica polymorphs. These results provide a comprehensive understanding of the structure-activity relationship between nearly free silanols and membranolytic activity of crystalline silica polymorphs, offering a possible clue for interpreting the molecular mechanisms associated with silica hazard and bio-minero-chemical interfacial phenomena, including prebiotic chemistry.

Lung inflammation induced by silica particles triggers hippocampal inflammation, synapse damage and memory impairment in mice

BACKGROUND

Considerable evidence indicates that a signaling crosstalk between the brain and periphery plays important roles in neurological disorders, and that both acute and chronic peripheral inflammation can produce brain changes leading to cognitive impairments. Recent clinical and epidemiological studies have revealed an increased risk of cognitive impairment and dementia in individuals with impaired pulmonary function. However, the mechanistic underpinnings of this association remain unknown. Exposure to SiO₂ (silica) particles triggers lung inflammation, including infiltration by peripheral immune cells and upregulation of pro-inflammatory cytokines. We here utilized a mouse model of lung silicosis to investigate the crosstalk between lung inflammation and memory.

METHODS

Silicosis was induced by intratracheal administration of a single dose of 2.5 mg SiO₂/kg in mice_. Molecular and behavioral measurements were conducted 24 h and 15 days after silica administration. Lung and hippocampal inflammation were investigated by histological analysis and by determination of pro-inflammatory cytokines. Hippocampal synapse damage, amyloid-β (Aβ) peptide content and phosphorylation of Akt, a proxy of hippocampal insulin signaling, were investigated by Western blotting and ELISA. Memory was assessed using the open field and novel object recognition tests.

RESULTS

Administration of silica induced alveolar collapse, lung infiltration by polymorphonuclear (PMN) cells, and increased lung pro-inflammatory cytokines. Lung inflammation was followed by upregulation of hippocampal pro-inflammatory cytokines, synapse damage, accumulation of the Aβ peptide, and memory impairment in mice.

CONCLUSION

The current study identified a crosstalk between lung and brain inflammatory responses leading to hippocampal synapse damage and memory impairment after exposure to a single low dose of silica in mice.

Think Beyond Particle Cytotoxicity: When Self-Cellular Components Released After Immunogenic Cell Death Explain Chronic Disease Development

The prolonged perturbation of the immune system following the release of a plethora of self-molecules (known as damage-associated molecular patterns, DAMPs) by stressed or dying cells triggers acute and chronic pathological responses. DAMPs are commonly released after plasma membrane damage or complete rupture due to immunogenic cell death (ICD), upon numerous stressors including infectious and toxic agents. The set of DAMPs released after ICD include mature proinflammatory cytokines and alarmins, but also polymeric macromolecules. These self-intracellular components are recognized by injured and healthy surrounding cells via innate receptors, and induce upregulation of stress-response mechanisms, including inflammation. In this review, by overstepping the simple toxicological evaluation, we apply ICD and DAMP concepts to silica cytotoxicity, providing new insights on the mechanisms driving the progress and/or the exacerbation of certain SiO2–related pathologies. Finally, by proposing self-DNA as new crucial DAMP, we aim to pave the way for the development of innovative and easy-to-perform predictive tests to better identify the hazard of fine and ultrafine silica particles. Importantly, such mechanisms could be extended to nano/micro plastics and diesel particles, providing strategic advice and reports on their health issues.

Tumor microenvironment regulation - enhanced radio - immunotherapy

Radiotherapy (RT) is frequently utilized for cancer treatment in clinical practice and has been proved to have immune stimulation potency in recent years. However, its inhibitory effect on tumor growth, especially on tumor metastasis, is still limited by many factors, including the complex tumor microenvironment (TME). Therefore, the TME - regulating SiO₂@MnO₂ nanoparticles (SM NPs) were prepared and applied to the combination of RT and immunotherapy. In a bilateral animal model, SM NPs not only enhanced the inhibitory effect of RT on primary tumor growth, but also strengthened the abscopal effect to inhibit the growth of distant untreated tumors. As for the distant untreated tumor, 40% of mice showed complete inhibition of tumor growth and 40% showed a suppressed tumor growth. Moreover, SM NPs showed modulation functions for TME through inducing the increase in intracellular levels of oxygen and reactive oxygen species after their reaction with hydrogen peroxide and the main antioxidative agent glutathione in TME. Lastly, SM NPs also effectively induced the increase in the amounts of cytokines secreted by macrophage - like cells, indicating modulation functions for immune responses. This work highlighted a potential strategy of simultaneously inhibiting tumor growth and metastasis through the regulation of TME and immune responses by SM NPs - enhanced radio - immunotherapy.

Protective effects of intranasal curcumin on silica-induced lung damage

OBJECTIVE

Being anti-inflammatory and an antioxidant in nature, curcumin has been studied for its anti-asthmatic effects, but its impact on silicosis has not been investigated before. It is a form of occupational lung illness caused by inhaling crystalline silica. It is particularly common among those who work in construction-related sectors. Therefore, present study has been undertaken to investigate impact of intranasal curcumin on silica induced lung damage in mice model of silicosis.

MATERIALS AND METHODS

Mice model of silicosis was developed by intranasal silica instillation (2.5 mg/mice) for different durations mainly 7, 14 and 21 days, where the longest duration of silica exposure (21 days) mimics chronic occupational exposure of silica dust leading to silicosis. Curcumin (5 mg/kg,i.n) and /or dexamethasone, a known corticosteroid (10 mg/kg,i.p) was administered an hour prior to silica administration.

RESULTS

Present study revealed silica induced lung damage in the mice model of silicosis characterized by airway inflammation, collagen deposition and enhanced expression of fibrosis markers (MMP-9, α-SMA, Hydroxyproline), which were significantly reduced in curcumin treatment groups. Inhibitory effects of curcumin were compared with standard drug, dexamethasone, a corticosteroid and was found better in protecting structural alterations in the lung. Damaged and abnormal mitochondria (enlarged and irregular shapes) were observed in silicosis group which were reduced in curcumin and dexamethasone treatment groups as revealed in transmission electron microscopic studies.

CONCLUSIONS

Present study shows protective effects of intranasal curcumin on silica-induced airway inflammation and structural changes thereby lung damage. Hence, it can be considered as an alternative and complementary medication for silicosis.

Inflammatory indices obtained from routine blood tests show an inflammatory state associated with disease progression in engineered stone silicosis patients

Patients with silicosis caused by occupational exposure to engineered stone (ES) present a rapid progression from simple silicosis (SS) to progressive massive fibrosis (PMF). Patient classification follows international rules based on radiology and high-resolution computed tomography (HRCT), but limited studies, if any, have explored biomarkers from routine clinical tests that can be used as predictors of disease status. Our objective was thus to investigate circulating biomarker levels and systemic inflammatory indices in ES silicosis patients whose exposure to ES dust ended several years ago. Ninety-one adult men, ex-workers in the manufacturing of ES, 53 diagnosed with SS and 38 with PMF, and 22 healthy male volunteers (HC) as controls not exposed to ES dust, were recruited. The following circulating levels of biomarkers like lactate dehydrogenase (LDH), angiotensin-converting-enzyme (ACE), protein C reactive (PCR), rheumatoid factor, alkaline phosphatase and fibrinogen were obtained from clinical reports after being measured from blood samples. As biochemical markers, only LDH (HC = 262 ± 48.1; SS = 315.4 ± 65.4; PMF = 337.6 ± 79.3 U/L), ACE (HC = 43.1 ± 18.4; SS = 78.2 ± 27.2; PMF = 86.1 ± 23.7 U/L) and fibrinogen (HC = 182.3 ± 49.1; SS = 212.2 ± 43.5; PMF = 256 ± 77.3 U/L) levels showed a significant sequential increase, not been observed for the rest of biomarkers, in the HC → SS → PMF direction. Moreover, several systemic inflammation indices neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR), platelet-to-lymphocyte ratio (PLR), systemic inflammation response index (SIRI), systemic immune-inflammation index (SII), aggregate index of systemic inflammation (AISI) derived from whole blood cell counts showed significant differences between the HC, SS and PMF groups. All these biomarkers were analyzed using receiver operating characteristic (ROC) curves, and the results provided moderately high sensitivity and specificity for discriminating between ES silicosis patient groups and healthy controls. Our study reveals that some inflammatory biomarkers, easily available from routine blood analysis, are present in ES silicosis patients even several years after cessation of exposure to ES silica dust and they could help to know the progression of the disease.

The significance of serum S100 calcium-binding protein A4 in silicosis

Background

Silicosis is a chronic occupational pulmonary disease characterized by persistent inflammation and irreversible fibrosis. Considerable evidences now indicate that S100 calcium-binding protein A4 (S100A4) has been associated with fibrotic diseases. However, the role of S100A4 in silicosis is still unclear.

Methods

In this study, serum levels of S100A4, transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) in patients with silicosis (n = 42) and control group (CG, n = 12) were measured by ELISA. S100A4 expression in lung tissues and primary alveolar macrophages (AMs) of mice with and without silicosis was detected by immunohistochemistry (IHC)/real-time PCR. The correlations between S100A4 and cytokines or lung function were assessed by Spearman's rank correlation analyses.

Results

Compared with CG, the levels of S100A4 were significantly increased in silicosis patients (70.84 (46.22, 102.46) ng/ml vs (49.84 (42.86, 60.02) ng/ml). The secretions of TGF-β1, CTGF, IL-6 and TNF-α in silicosis group were significantly higher than that in control group (p < 0.05). Serum S100A4 levels were positively correlated with TGF-β1 and IL-6, while were negatively correlated with lung function parameters including percentage of predicted forced vital capacity (FVC%pre), maximum vital capacity (Vcmax), deep inspiratory capacity (IC) and peak expiratory flow at 75% of vital capacity (PEF75). In receiver operating characteristic (ROC) analyses, S100A4 > 61.7 ng/ml had 63.4% sensitivity and 83.3% specificity for silicosis, and the area under the curve (AUC) was 0.707. Furthermore, immunostaining of lung tissues showed the accumulation of S100A4-positive cells in the areas of nodules of silicotic mice. The mRNA expression of S100A4 in the lung tissues and AMs of silicotic mice were significantly higher than controls.

Conclusion

These data suggested that increased S100A4 might contribute to the pathogenesis of silicosis.

Fetal Liver-Derived Alveolar-like Macrophages: A Self-Replicating Ex Vivo Model of Alveolar Macrophages for Functional Genetic Studies

Alveolar macrophages (AMs) are tissue-resident cells in the lungs derived from the fetal liver that maintain lung homeostasis and respond to inhaled stimuli. Although the importance of AMs is undisputed, they remain refractory to standard experimental approaches and high-throughput functional genetics, as they are challenging to isolate and rapidly lose AM properties in standard culture. This limitation hinders our understanding of key regulatory mechanisms that control AM maintenance and function. In this study, we describe the development of a new model, fetal liver-derived alveolar-like macrophages (FLAMs), which maintains cellular morphologies, expression profiles, and functional mechanisms similar to murine AMs. FLAMs combine treatment with two key cytokines for AM maintenance, GM-CSF and TGF-β. We leveraged the long-term stability of FLAMs to develop functional genetic tools using CRISPR-Cas9-mediated gene editing. Targeted editing confirmed the role of AM-specific gene Marco and the IL-1 receptor Il1r1 in modulating the AM response to crystalline silica. Furthermore, a genome-wide knockout library using FLAMs identified novel genes required for surface expression of the AM marker Siglec-F, most notably those related to the peroxisome. Taken together, our results suggest that FLAMs are a stable, self-replicating model of AM function that enables previously impossible global genetic approaches to define the underlying mechanisms of AM maintenance and function.

Silica Induction of Diverse Inflammatory Proteome in Lungs of Lupus-Prone Mice Quelled by Dietary Docosahexaenoic Acid Supplementation

Repeated short-term intranasal instillation of lupus-prone mice with crystalline silica (cSiO2) induces inflammatory gene expression and ectopic lymphoid neogenesis in the lung, leading to early onset of systemic autoimmunity and rapid progression to glomerulonephritis. These responses are suppressed by dietary supplementation with the ω-3 polyunsaturated fatty acid docosahexaenoic acid (DHA). Here, we tested the hypothesis that dietary DHA supplementation suppresses cSiO2-induced inflammatory proteins in bronchoalveolar alveolar lavage fluid (BALF) and plasma of lupus-prone mice. Archived tissue fluid samples were used from a prior investigation in which 6 wk-old lupus-prone female NZBWF1 mice were fed isocaloric diets containing 0 or 10 g/kg DHA for 2 wks and then intranasally instilled with 1 mg cSiO2 or vehicle once weekly for 4 wks. Cohorts were terminated at 1, 5, 9 or 13 wk post-instillation (PI). BALF and plasma from each cohort were analyzed by high density multiplex array profiling of 200 inflammatory proteins. cSiO2 time-dependently induced increases in the BALF protein signatures that were highly reflective of unresolved lung inflammation, although responses in the plasma were much less robust. Induced proteins in BALF included chemokines (e.g., MIP-2, MCP-5), enzymes (e.g., MMP-10, granzyme B), adhesion molecules (e.g., sE-selectin, sVCAM-1), co-stimulatory molecules (e.g., sCD40L, sCD48), TNF superfamily proteins (e.g., sTNFRI, sBAFF-R), growth factors (e.g., IGF-1, IGFBP-3), and signal transduction proteins (e.g., MFG-E8, FcgRIIB), many of which were blocked or delayed by DHA supplementation. The BALF inflammatory proteome correlated positively with prior measurements of gene expression, pulmonary ectopic lymphoid tissue neogenesis, and induction of autoantibodies in the lungs of the control and treatment groups. Ingenuity Pathway Analysis (IPA) revealed that IL-1β, TNF-α, and IL-6 were among the top upstream regulators of the cSiO2-induced protein response. Furthermore, DHA's effects were associated with downregulation of cSiO2-induced pathways involving i) inhibition of ARE-mediated mRNA decay, ii) bacterial and viral pattern recognition receptor activation, or iii) TREM1, STAT3, NF-κB, and VEGF signaling and with upregulation of PPAR, LXR/RXR and PPARα/RXRα signaling. Altogether, these preclinical findings further support the contention that dietary DHA supplementation could be applicable as an intervention against inflammation-driven autoimmune triggering by cSiO2 or potentially other environmental agents.

ZC3H4 promotes pulmonary fibrosis via an ER stress-related positive feedback loop

BACKGROUND

Pulmonary fibrosis is a sequela of many pulmonary diseases, such as pneumoconiosis and idiopathic pulmonary fibrosis. The principal characteristics of pulmonary fibrosis comprise myofibroblast proliferation, alveolar damage and deposition of extracellular matrix components, which cause abnormal lung structure remodeling and an irreversible decline in lung function; however, the detailed mechanisms remain unclear. The current study focused on the role of ZC3H4, a new member of the zinc finger protein family, in SiO₂-induced pulmonary fibrosis.

METHODS

The expression of ZC3H4 and fibroblast activation markers (COL1A1, COL3A1 and ACTA1) was measured by western blotting and immunofluorescence staining after SiO₂ exposure (50 μg/cm²). The functional change in fibroblasts was studied with a scratch assay and a 3D migration assay. The CRISPR/Cas9 system was used to explore the regulatory mechanisms of ZC3H4 in pulmonary fibroblast cells.

RESULTS

The expression levels of ZC3H4 and sigmar1 (a key regulator of ER stress) were increased in pulmonary fibroblast cells and were associated with fibroblast activation, as indicated by the increase in COL1A1, COL3A1 and ACTA1, as well as the migration ability. SiO₂-enhanced fibroblast activation was attenuated by specific knockdown of ZC3H4 and inhibition of ER stress, demonstrating that ZC3H4 activated fibroblasts via the sigmar1/ER stress pathway. Interestingly, ER stress blockade also inhibited ZC3H4 expression, indicating the positive feedback regulatory mechanism of ER stress on ZC3H4.

CONCLUSIONS

Our results demonstrate that ZC3H4 and sigmar1 might act as novel therapeutic targets for silicosis, providing a reference for further pulmonary fibrosis research.

PPARγ/LXRα axis mediated phenotypic plasticity of lung fibroblasts in silica-induced experimental silicosis

Silicosis is a disease mainly caused by pulmonary interstitial fibrosis caused by long-term inhalation of dust with excessively high content of free SiO₂. Transdifferentiation of lung fibroblasts into myofibroblasts is an important cellular basis for silicosis, but the key transcription factors (TFs) involved in this process are still unclear. In order to explore the biological regulation of transcription factor PPARγ/LXRα in silica-induced pulmonary fibrosis, this study explored the molecular mechanism of PPARγ/LXRα involved in regulating transcription factors related to SiO₂-induced lung injury at the cellular level and in animal models. ChIP-qPCR detected that PPARγ directly regulated the transcriptional activity of the LXRα gene promoter, while the PPARγ agonist RSG increased the expression of LXRα. In addition, we demonstrated in the cell model that upregulation of LXRα can inhibit silica-mediated fibroblast transdifferentiation, accompanied by an increase in the expression of SREBF1, PLTP and ABCA1. The results of LXRα silencing experiment matched those of overexpression experiment. These studies explored the role of LXRα in plasticity and phenotypic transformation between lung fibroblasts and myofibroblasts. Therefore, inhibiting or reversing the transdifferentiation of lung fibroblasts to myofibroblasts by intervening PPARγ/LXRα may provide a new therapeutic target for the treatment of silicosis.

Silicon, an important exposure marker in vivo in silicosis research

PURPOSE

The degree of silicosis exposure is closely related to the progress of silicosis. At present, we use animal and human studies to explore whether silicon can be an important exposure marker in the development of silicosis.

METHODS

Rats were randomly divided into 2 groups: (1) controls; and (2) silicosis. Rats in the silicosis group were killed at 4, 8, 12, 16, 24 h, 3, 7, 14, 21, and 28 days. Hematoxylin-eosin (HE) and immunohistochemistry (IHC) were performed to observe the histomorphology of lung tissue. The expression levels of CC16 and SP-D were detected using ELISA kits. In addition, we conducted a population study. Workers who have been selected to work in an iron mine for more than 1 year as research objects. The population was divided into four groups: silicosis exposure group (workers exposed to silica dust for more than 1 year in an iron mine were selected); patients group (silicosis patients); observation group (evidence of disease not meeting formal diagnostic criteria) and control group. Both the levels of trace silicon in the urine and blood of rats and human subjects were measured with ICP-MS.

RESULTS

Serum levels of silicon were immediately increased in rats exposed to silicon dust. Similarly, our population study revealed that the silicon level in the silica exposure group and the observing group (exposed but no obvious symptoms) were significantly increased over that of the control group (P < 0.05). In subjects with extended exposure to silica, the serum and urine silicon level in exposed workers appeared to rapidly increase, reaching its peak in 1-5 years, followed by a gradual decline thereafter. Workers exposed to dust for less than 10 years were divided into subgroups by 2-year limit. The levels of serum silicon, urine silicon, TGF-β1, and TNF-α were significantly higher than that of control group.

CONCLUSION

Changes of the serum levels of silicon occurred earlier than the expression of cytokines such as TNF-α, TGF-β1, CC16, and SP-D. The level of silicon in workers rapidly increased after exposure to silica, and the change occurred before the expression of TGF-β1 and TNF-α. As a whole, the findings suggest that determining the level of silicon in vivo might be an effective exposure marker in the diagnosis and pathogenesis of silicosis.

Pulmonary inflammatory and fibrogenic response induced by graphitized multi-walled carbon nanotube involved in cGAS-STING signaling pathway

Graphitized multi-walled carbon nanotubes (GMWCNTs) are a new type of nanomaterial. Recently, their production and application in biological medicine have grown rapidly. However, GMWCNTs may cause adverse health effects, including the common occupational disease of pulmonary fibrosis. Pulmonary fibrosis is a serious progressive disease that often leads to lung failure, high mortality, and disability, and there is no effective therapy currently available. Therefore, identifying new biomarkers of the disease is important to better understand the disease mechanisms and explore new therapeutic strategies. In this study, 40 μg of GMWCNTs was used to treat mice in vivo by pharyngeal aspiration, and different genes were screened by transcriptome sequencing. Activation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) signal pathway had an important effect on the development of pulmonary inflammation and fibrosis. GMWCNTs were then administered to the mice with a STING inhibitor (C-176). Inhibition of STING effectively decreased pulmonary inflammation and fibrosis in mice induced by GMWCNTs. Collectively, activation of the cGAS-STING signaling pathway is involved in GMWCNT-induced pulmonary inflammation and fibrosis in mice.

Serum levels of inflammatory mediators as prognostic biomarker in silica exposed workers

Silicosis is a diffuse interstitial lung disease caused by sustained inhalation of silica and silicates. Several cytokines are activated by their inhalation and can mediate the process of pulmonary fibrosis. The identification of biomarkers could allow an early diagnosis before the development of radiological alterations and help monitor the evolution of patients. The objetive of this study was to determine the clinical significance of specific biomarkers, to estimate their association with the development, severity and/or progression of silicosis, and identify determinants of this evolution. We conducted a prospective observational study in patients attending the pulmonology clinic from 2009 to 2018. Serum levels of the following inflammatory mediators were assessed: interleukin-6 (IL-6), interleukin 2 receptor subunit alpha (IL2R) interleukin 1 beta (IL1B), interleukin-8 (IL-8), tumour necrosis factor-alpha (TNF-α), transforming growth factor-beta1 (TGF-β1), alpha-1 antitrypsin (AAT), C-reactive protein (CRP), lactate dehydrogenase (LDH) and ferritin in subjects exposed to silica, with and without silicosis. Association between those inflammatory mediators with lung function measurements and radiological severity of disease and their impact on prognosis were analysed. 337 exposed to silica (278 with silicosis) and 30 subjects in the control group were included. IL-8, α1AT, ferritin, CRP and LDH levels were higher in silicosis than in those exposed to silica without silicosis. IL-8, LDH and AAT levels were associated with progression of silicosis and IL-6, IL-8, LDH, AAT, ferritin, and CRP with vital status. The results of the ROC analysis indicated the potential of IL-8 as a biomarker in the presence of silicosis and for the prediction of mortality.

The effect of short silica fibers (0.3 μm 3.2 μm) on macrophages

Silica fibers with a dimension of 0.3 μm ∙ 3.2 μm² nm were prepared by a modified Stöber synthesis as model particles. The particles were characterized by scanning electron microscopy, elemental analysis, thermogravimetry and X-ray powder diffraction. Their uptake by macrophages (THP-1 cells and NR8383 cells) was studied by confocal laser scanning microscopy and scanning electron microscopy. The uptake by cells was very high, but the silica fibers were not harmful to NR8383 cells in concentrations up to 100 μg mL^-1. Only above 100 μg mL^-1, significant cell toxic effects were observed, probably induced by a high dose of particles that had sedimented on the cells and led to the adverse effects. The chemotactic response as assessed by the particle-induced migration assay (PICMA) was weak in comparison to a control of agglomerated silica particles. The as-prepared fibers were fully X-ray amorphous but crystallized to β-cristobalite after heating to 1000 °C and converted to α-cristobalite upon cooling to ambient temperature. The fibers had sintered to larger aggregates but retained their elongated primary shape. The particle cytotoxicity towards THP-1 cells was not significantly enhanced by the crystallization.

Omega-3 Polyunsaturated Fatty Acid Intervention Against Established Autoimmunity in a Murine Model of Toxicant-Triggered Lupus

Workplace exposure to respirable crystalline silica dust (cSiO2) has been etiologically linked to the development of lupus and other human autoimmune diseases. Lupus triggering can be recapitulated in female NZBWF1 mice by four weekly intranasal instillations with 1 mg cSiO2. This elicits inflammatory/autoimmune gene expression and ectopic lymphoid structure (ELS) development in the lung within 1 week, ultimately driving early onset of systemic autoimmunity and glomerulonephritis. Intriguingly, dietary supplementation with docosahexaenoic acid (DHA), an ω-3 polyunsaturated fatty acid (PUFA) found in fish oil, beginning 2 week prior to cSiO2 challenge, prevented inflammation and autoimmune flaring in this novel model. However, it is not yet known how ω-3 PUFA intervention influences established autoimmunity in this murine model of toxicant-triggered lupus. Here we tested the hypothesis that DHA intervention after cSiO2-initiated intrapulmonary autoimmunity will suppress lupus progression in the NZBWF1 mouse. Six-week old NZWBF1 female mice were fed purified isocaloric diet for 2 weeks and then intranasally instilled with 1 mg cSiO2 or saline vehicle weekly for 4 consecutive weeks. One week after the final instillation, which marks onset of ELS formation, mice were fed diets supplemented with 0, 4, or 10 g/kg DHA. One cohort of mice (n = 8/group) was terminated 13 weeks after the last cSiO2 instillation and assessed for autoimmune hallmarks. A second cohort of mice (n = 8/group) remained on experimental diets and was monitored for proteinuria and moribund criteria to ascertain progression of glomerulonephritis and survival, respectively. DHA consumption dose-dependently increased ω-3 PUFA content in the plasma, lung, and kidney at the expense of the ω-6 PUFA arachidonic acid. Dietary intervention with high but not low DHA after cSiO2 treatment suppressed or delayed: (i) recruitment of T cells and B cells to the lung, (ii) development of pulmonary ELS, (iii) elevation of a wide spectrum of plasma autoantibodies associated with lupus and other autoimmune diseases, (iv) initiation and progression of glomerulonephritis, and (v) onset of the moribund state. Taken together, these preclinical findings suggest that DHA supplementation at a human caloric equivalent of 5 g/d was an effective therapeutic regimen for slowing progression of established autoimmunity triggered by the environmental toxicant cSiO2.

The UFSP2/UFMylation Pathway Is Involved in Silica-Induced Pulmonary Injury

Silicosis is an irreversible occupational pulmonary disease that is characterized as progressed pulmonary fibrosis. In this study, we investigated the changes of UFSP2 and the related UFMylation in silica-induced pulmonary injury mice models. The experimental silicosis models were prepared by intratracheal injection of silica particles, and the lung samples were harvested at the first or the seventh day after treatment. We found that the UFSP2 expression in the 1-day models was comparable, whereas it was upregulated in the 7-day models. Consistently, the UFMylation in the lung tissues of the 7-day models was activated. In addition, we observed the CADM2, an adhesion molecule, was reported to associate with epithelial-mesenchymal transition, was upregulated in the lungs of 7-day models. In contrast, it remained comparable in the 1-day models. Our data indicated that the UFSP2/UFMylation pathway and the CADM2 might be involved in the silica-induced pulmonary injury.

The expanding role of CDR1-AS in the regulation and development of cancer and human diseases

CircRNAs are a superabundant and highly conserved group of noncoding RNAs (ncRNAs) that are characterized by their high stability and integrity compared with linear forms of ncRNAs. Recently, their critical role in gene expression regulation has been shown; thus, it is not far-fetched to believe that their abnormal expression can be a cause of different kinds of diseases such as cancer, neurodegenerative, and autoimmune diseases. They can have a function in variety of biological processes such as microRNA (miRNA) sponging, interacting with RNA-binding proteins, or even an ability to translate to proteins. A huge challenge in finding diagnostic biomarkers is finding noninvasive biomarkers that can be detected in human fluids, especially blood samples. CircRNAs are becoming candidate biomarkers for diagnosis and prognosis of these diseases through their ability to transverse from the blood-brain barrier and their broad presence in circulating exosomes. The circRNA for miRNA-7 (ciRS-7) is newly recognized, and acknowledged to being related to human pathology and cancer progression. In this review, we first briefly summarize the latest studies about their characteristics, biogenesis, and their mechanisms of action in the regulation and development of human diseases. Finally, we provide a list of diseases that are linked to one member of this novel class of ncRNAs called ciRS-7.

Hesperetin attenuates silica-induced lung injury by reducing oxidative damage and inflammatory response

Oxidative stress and the inflammatory response are two important mechanisms of silica-induced lung injury. Hesperetin (HSP) is a natural flavonoid compound that is found in citrus fruits and has been indicated to exhibit strong antioxidant and anti-inflammatory properties. The current study evaluated the protective effect of HSP on lung injury in rats exposed to silica. The results indicated that the degree of alveolitis and pulmonary fibrosis in the HSP-treated group was significantly decreased compared with the silica model group. The content of hydroxyproline (HYP) was also revealed to decrease overall in the HSP treated group compared with the silica model group, indicating that the degree of pulmonary fibrosis was decreased compared with the silica model group. The present study also demonstrated that HSP reduced oxidation levels of malondialdehyde (MDA) and increased the activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-PX). Total antioxidant capacity (T-AOC) was also increased following HSP treatment, indicating that HSP can alleviate oxidative stress in the lung tissue of silica-exposed rats. In addition, HSP was revealed to inhibit the synthesis and secretion of fibrogenic factor TGF-β1, reduce the production of pro-inflammatory cytokines IL-1β, IL-4, TNF-α and increase the levels of anti-inflammatory factors IFN-γ and IL-10. The current study demonstrated that HSP can effectively attenuate silica-induced lung injury by reducing oxidative damage and the inflammatory response.

Perspective: The Lung, Particles, Fibers, Nanomaterials, and Autoimmunity

Studies have shown that a wide range of factors including drugs, chemicals, microbes, and other environmental agents can induce pre-clinical autoimmunity. However, only a few have been confidently linked to autoimmune diseases. Among these are exposures to inhaled particulates that are known to be associated with autoimmune diseases such as lupus and rheumatoid arthritis. In this article, the potential of particle, fiber, and nanomaterial exposures to induce autoimmunity is discussed. It is hypothesized that inhalation of particulate material known to be associated with human autoimmune diseases, such as cigarette smoke and crystalline silica, results in a complex interplay of a number of pathological processes, including, toxicity, oxidative stress, cell and tissue damage, chronic inflammation, post-translational modification of self-antigens, and the formation of lymphoid follicles that provide a milieu for the accumulation of autoreactive B and T cells necessary for the development and persistence of autoimmune responses, leading to disease. Although experimental studies show nanomaterials are capable of inducing several of the above features, there is no evidence that this matures to autoimmune disease. The procession of events hypothesized here provides a foundation from which to pursue experimental studies to determine the potential of other environmental exposures to induce autoimmunity and autoimmune disease.

Pulmonary toxicants and fibrosis: innate and adaptive immune mechanisms

Pulmonary fibrosis is characterized by destruction and remodeling of the lung due to an accumulation of collagen and other extracellular matrix components in the tissue. This results in progressive irreversible decreases in lung capacity, impaired gas exchange and eventually, hypoxemia. A number of inhaled and systemic toxicants including bleomycin, silica, asbestos, nanoparticles, mustard vesicants, nitrofurantoin, amiodarone, and ionizing radiation have been identified. In this article, we review the role of innate and adaptive immune cells and mediators they release in the pathogenesis of fibrotic pathologies induced by pulmonary toxicants. A better understanding of the pathogenic mechanisms underlying fibrogenesis may lead to the development of new therapeutic approaches for patients with these debilitating and largely irreversible chronic diseases.

Biological effects of inhaled hydraulic fracturing sand dust. IV. Pulmonary effects

Hydraulic fracturing creates fissures in subterranean rock to increase the flow and retrieval of natural gas. Sand ("proppant") in fracking fluid injected into the well bore maintains fissure patency. Fracking sand dust (FSD) is generated during manipulation of sand to prepare the fracking fluid. Containing respirable crystalline silica, FSD could pose hazards similar to those found in work sites where silica inhalation induces lung disease such as silicosis. This study was performed to evaluate the possible toxic effects following inhalation of a FSD (FSD 8) in the lung and airways. Rats were exposed (6 h/d × 4 d) to 10 or 30 mg/m3 of a FSD collected at a gas well, and measurements were performed 1, 7, 27 and, in one series of experiments, 90 d post-exposure. The following ventilatory and non-ventilatory parameters were measured in vivo and/or in vitro: 1) lung mechanics (respiratory system resistance and elastance, tissue damping, tissue elastance, Newtonian resistance and hysteresivity); 2) airway reactivity to inhaled methacholine (MCh); airway epithelium integrity (isolated, perfused trachea); airway efferent motor nerve activity (electric field stimulation in vitro); airway smooth muscle contractility; ion transport in intact and cultured epithelium; airway effector and sensory nerves; tracheal particle deposition; and neurogenic inflammation/vascular permeability. FSD 8 was without large effect on most parameters, and was not pro-inflammatory, as judged histologically and in cultured epithelial cells, but increased reactivity to inhaled MCh at some post-exposure time points and affected Na+ transport in airway epithelial cells.

Subtoxic cell responses to silica particles with different size and shape

Health risks from particles are a priority challenge to health protection at work. Despite the ubiquitous exposure to a wide range of particles and the many years of research in this field, there are fundamental unresolved questions regarding the prevention of particle-related respiratory diseases. Here, the highly relevant particulate material silicon dioxide was analyzed with emphasis on defined size and shape. Silica particles were prepared with different size and shape: Spheres (NS nanospheres 60 nm; SMS submicrospheres 230 nm; MS microspheres 430 nm) and rods (SMR submicrorods with d = 125 nm, L = 230 nm; aspect ratio 1:1.8; MR microrods with d = 100 nm, L = 600 nm; aspect ratio 1:6). After an in-depth physicochemical characterization, their effects on NR8383 alveolar macrophages were investigated. The particles were X-ray amorphous, well dispersed, and not agglomerated. Toxic effects were only observed at high concentrations, i.e. ≥ 200 µg mL-1, with the microparticles showing a stronger significant effect on toxicity (MS≈MR > SMR≈SMS≈NS) than the nanoparticles. Special attention was directed to effects in the subtoxic range (less than 50% cell death compared to untreated cells), i.e. below 100 µg mL-1 where chronic health effects may be expected. All particles were readily taken up by NR8383 cells within a few hours and mainly found associated with endolysosomes. At subtoxic levels, neither particle type induced strongly adverse effects, as probed by viability tests, detection of reactive oxygen species (ROS), protein microarrays, and cytokine release (IL-1β, GDF-15, TNF-α, CXCL1). In the particle-induced cell migration assay (PICMA) with leukocytes (dHL-60 cells) and in cytokine release assays, only small effects were seen. In conclusion, at subtoxic concentrations, where chronic health effects may be expected, neither size and nor shape of the synthesized chemically identical silica particles showed harmful cell-biological effects.

Biological effects of inhaled hydraulic fracturing sand dust. III. Cytotoxicity and pro-inflammatory responses in cultured murine macrophage cells

Cultured murine macrophages (RAW 264.7) were used to investigate the effects of fracking sand dust (FSD) for its pro-inflammatory activity, in order to gain insight into the potential toxicity to workers associated with inhalation of FSD during hydraulic fracturing. While the role of respirable crystalline silica in the development of silicosis is well documented, nothing is known about the toxicity of inhaled FSD. The FSD (FSD 8) used in these studies was from an unconventional gas well drilling site. FSD 8was prepared as a 10 mg/ml stock solution in sterile PBS, vortexed for 15 s, and allowed to sit at room temperature for 30 min before applying the suspension to RAW 264.7cells. Compared to PBS controls, cellular viability was significantly decreased after a 24 h exposure to FSD. Intracellular reactive oxygen species (ROS) production and the production of IL-6, TNFα, and endothelin-1 (ET-1) were up-regulated as a result of the exposure, whereas the hydroxyl radical (.OH) was only detected in an acellular system. Immunofluorescent staining of cells against TNFα revealed that FSD 8 caused cellular blebbing, and engulfment of FSD 8 by macrophages was observed with enhanced dark-field microscopy. The observed changes in cellular viability, cellular morphology, free radical generation and cytokine production all confirm that FSD 8 is cytotoxic to RAW 264.7 cells and warrants future studies into the specific pathways and mechanisms by which these toxicities occur.

Cell-biological effects of zinc oxide spheres and rods from the nano- to the microscale at sub-toxic levels

Zinc oxide particles were synthesized in various sizes and shapes, i.e., spheres of 40-nm, 200-nm, and 500-nm diameter and rods of 40∙100 nm² and 100∙400 nm² (all PVP-stabilized and well dispersed in water and cell culture medium). Crystallographically, the particles consisted of the hexagonal wurtzite phase with a primary crystallite size of 20 to 100 nm. The particles showed a slow dissolution in water and cell culture medium (both neutral; about 10% after 5 days) but dissolved within about 1 h in two different simulated lysosomal media (pH 4.5 to 4.8). Cells relevant for respiratory exposure (NR8383 rat alveolar macrophages) were exposed to these particles in vitro. Viability, apoptosis, and cell activation (generation of reactive oxygen species, ROS, release of cytokines) were investigated in an in vitro lung cell model with respect to the migration of inflammatory cells. All particle types were rapidly taken up by the cells, leading to an increased intracellular zinc ion concentration. The nanoparticles were more cytotoxic than the microparticles and comparable with dissolved zinc acetate. All particles induced cell apoptosis, unlike dissolved zinc acetate, indicating a particle-related mechanism. Microparticles induced a stronger formation of reactive oxygen species than smaller particles probably due to higher sedimentation (cell-to-particle contact) of microparticles in contrast to nanoparticles. The effect of particle types on the cytokine release was weak and mainly resulted in a decrease as shown by a protein microarray. In the particle-induced cell migration assay (PICMA), all particles had a lower effect than dissolved zinc acetate. In conclusion, the biological effects of zinc oxide particles in the sub-toxic range are caused by zinc ions after intracellular dissolution, by cell-to-particle contacts, and by the uptake of zinc oxide particles into cells.

Endoplasmic Reticulum Stress Provocation by Different Nanoparticles: An Innovative Approach to Manage the Cancer and Other Common Diseases

A proper execution of basic cellular functions requires well-controlled homeostasis including correct protein folding. Endoplasmic reticulum (ER) implements such functions by protein reshaping and post-translational modifications. Different insults imposed on cells could lead to ER stress-mediated signaling pathways, collectively called the unfolded protein response (UPR). ER stress is also closely linked with oxidative stress, which is a common feature of diseases such as stroke, neurodegeneration, inflammation, metabolic diseases, and cancer. The level of ER stress is higher in cancer cells, indicating that such cells are already struggling to survive. Prolonged ER stress in cancer cells is like an Achilles' heel, if aggravated by different agents including nanoparticles (NPs) may be exhausted off the pro-survival features and can be easily subjected to proapoptotic mode. Different types of NPs including silver, gold, silica, graphene, etc. have been used to augment the cytotoxicity by promoting ER stress-mediated cell death. The diverse physico-chemical properties of NPs play a great role in their biomedical applications. Some special NPs have been effectively used to address different types of cancers as these particles can be used as both toxicological or therapeutic agents. Several types of NPs, and anticancer drug nano-formulations have been engineered to target tumor cells to enhance their ER stress to promote their death. Therefore, mitigating ER stress in cancer cells in favor of cell death by ER-specific NPs is extremely important in future therapeutics and understanding the underlying mechanism of how cancer cells can respond to NP induced ER stress is a good choice for the development of novel therapeutics. Thus, in depth focus on NP-mediated ER stress will be helpful to boost up developing novel pro-drug candidates for triggering pro-death pathways in different cancers.

Omega-3 Docosahexaenoic Acid (DHA) Impedes Silica-Induced Macrophage Corpse Accumulation by Attenuating Cell Death and Potentiating Efferocytosis

Airway exposure of lupus-prone NZBWF1 mice to crystalline silica (cSiO₂), a known trigger of human autoimmune disease, elicits sterile inflammation and alveolar macrophage death in the lung that, in turn, induces early autoimmune onset and accelerates lupus progression to fatal glomerulonephritis. Dietary supplementation with docosahexaenoic acid (DHA), a marine ω-3 polyunsaturated fatty acid (PUFA), markedly ameliorates cSiO₂-triggered pulmonary, systemic, and renal manifestations of lupus. Here, we tested the hypothesis that DHA influences both cSiO₂-induced death and efferocytotic clearance of resultant cell corpses using three murine macrophage models: (i) primary alveolar macrophages (AM) isolated from NZBWF1 mice; (ii) self-renewing AM-like Max Planck Institute (MPI) cells isolated from fetuses of C57BL/6 mice, and (iii) RAW 264.7 murine macrophages, a virus-transformed cell line derived from BALB/c mice stably transfected with the inflammasome adaptor protein ASC (RAW-ASC). Incubation with cSiO₂ at 25 and 50 μg/ml for 6 h was found to dose-dependently induce cell death (p < 0.05) in all three models as determined by both acridine orange/propidium iodide staining and release of lactate dehydrogenase into cell culture supernatant. Pre-incubation with DHA at a physiologically relevant concentration (25 μM) significantly reduced cSiO₂-induced death (p < 0.05) in all three models. Cell death induction by cSiO₂ alone and its suppression by DHA were primarily associated with caspase-3/7 activation, suggestive of apoptosis, in AM, MPI, and RAW-ASC cells. Fluorescence microscopy revealed that all three macrophage models were similarly capable of efferocytosing RAW-ASC target cell corpses. Furthermore, MPI effector cells could likewise engulf RAW-ASC target cell corpses elicited by treatment with staurosporine (apoptosis), LPS, and nigericin (pyroptosis), or cSiO₂. Pre-incubation of RAW-ASC target cells with 25 μM DHA prior to death induced by these agents significantly enhanced their efferocytosis (p < 0.05) by MPI effector cells. In contrast, pre-incubating MPI effector cells with DHA did not affect engulfment of RAW-ASC target cells pre-incubated with vehicle. Taken together, these findings indicate that DHA at a physiologically relevant concentration was capable of attenuating macrophage death and could potentiate efferocytosis, with the net effect of reducing accumulation of cell corpses capable of eliciting autoimmunity.

Is individual genetic susceptibility a link between silica exposure and development or severity of silicosis? A systematic review

BACKGROUND

Silicosis is a lung disease of fibrotic nature resulting from the inhalation and deposition of dust containing crystalline silica. Subjects exposed to the same environmental factors may show distinct radiological manifestations, and since silicosis is known as a multifactorial disease, it is plausible that individual genetic susceptibility may play a role in the pathology. This review of the literature aims to provide an assessment of the present data on the genetic association studies in silicosis and describe the genes that potentially might influence silicosis susceptibility in silica-exposed individuals.

METHODS

We accessed the database of PubMed for articles published in English about interindividual genetic susceptibility to silicosis using terms related to the subject matter.

RESULTS

Following the evaluation process, 28 studies were included in this systematic review, including 23 original studies and 5 meta-analyses.

CONCLUSIONS

Regardless of the advances in the knowledge of the importance of gene variations in silicosis, more studies need to be performed, in particular, special polygenic and genome-wide investigations.

Mechanisms of Environment-Induced Autoimmunity

Although numerous environmental exposures have been suggested as triggers for preclinical autoimmunity, only a few have been confidently linked to autoimmune diseases. For disease-associated exposures, the lung is a common site where chronic exposure results in cellular toxicity, tissue damage, inflammation, and fibrosis. These features are exacerbated by exposures to particulate material, which hampers clearance and degradation, thus facilitating persistent inflammation. Coincident with exposure and resulting pathological processes is the posttranslational modification of self-antigens, which, in concert with the formation of tertiary lymphoid structures containing abundant B cells, is thought to promote the generation of autoantibodies that in some instances demonstrate major histocompatibility complex restriction. Under appropriate gene-environment interactions, these responses can have diagnostic specificity. Greater insight into the molecular and cellular requirements governing this process, especially those that distinguish preclinical autoimmunity from clinical autoimmunedisease, may facilitate determination of the significance of environmental exposures in human autoimmune disease.

Fullerene nanoparticles: a promising candidate for the alleviation of silicosis-associated pulmonary inflammation

Chronic exposure to crystalline silica causes the development of silicosis, which is one of the most important occupational diseases worldwide. In the early stage of silicosis, inhaled silica crystals initiate oxidative stress, a cycle of persistent inflammation and lung injury. And it is crucial to prevent the deteriorative progression in the onset of the disease. Herein, we present a promising candidate for the treatment of crystalline silica-induced pulmonary inflammation, using a silicosis mouse model caused by intratracheal instillation based on local administration of β-alanine and hydroxyl functionalized C70 fullerene nanoparticles (FNs). The results demonstrate that FNs could significantly alleviate inflammatory cells infiltration, lower the secretion of pro-inflammatory cytokines, and reduce the destruction of lung architecture stimulated by crystalline silica. Further investigations reveal that FNs could effectively inhibit the activation of NLRP3 (NACHT, LRR and PYD domains-containing protein 3) inflammasome, and thus prevent the secretion of mature IL-1β and neutrophil influx, deriving from the superior ROS scavenging capability. Importantly, FNs could not cause any obvious toxicity after pulmonary administration.

Transcriptome profile analysis reveals a silica-induced immune response and fibrosis in a silicosis rat model

Silicosis is a type of pneumoconiosis caused by the inhalation of silica dust. It is characterized by inflammation and fibrosis of the lung. Although many studies have reported that crystalline silica-inhalation into the lung initiates the immune response, activating effector cells and triggering the inflammatory cascade with subsequent elaboration of the extracellular matrix and fibrosis, the mechanism of silicosis pathogenesis remains unclear. In the present study, we established a silica inhalation-induced silicosis rat model validated by histological and cytokine analyses. RNA-seq and bioinformatic analyses showed that 600 genes were upregulated and 537 genes were downregulated in the silica-treated group. GO enrichment analysis indicates that these differentially expressed genes are enriched in several biological processes including immune response and organism remodeling. KEGG enrichment analysis showed that 53 enriched pathways were mainly associated with human diseases, immune response, signal transduction, and fibrosis process. Since alternative splicing of pre-mRNAs is also essential for the regulation of gene expression, we identified several alternative pre-mRNA splicing events in the fibrotic process. This study will provide a foundation to understand the molecular mechanism of the pulmonary fibrosis caused by silica.

In situ evidence of collagen V and signaling pathway of found inflammatory zone 1 (FIZZ1) is associated with silicotic granuloma in lung mice

Inhalation of silica particles causes silicosis: an occupational lung disease characterized by persistent inflammation with granuloma formation that leads to tissue remodeling and impairment of lung function. Although silicosis has been studied intensely, little is known about the crucial cellular mechanisms that initiate and drive the process of inflammation and fibrosis. Recently, found in inflammatory zone 1 (FIZZ1) protein, produced by alveolar macrophages and fibroblasts have been shown to induce the proliferation of myofibroblasts and their transdifferentiation, causing tissue fibrosis. Moreover, autoimmunogenic collagen V, produced by alveolar epithelial cells and fibroblasts, is involved in the pathophysiology of interstitial pulmonary fibrosis and bleomycin-induced lung fibrosis. Based on the aforementioned we hypothesized that FIZZ1 and collagen V may be involved in the silicotic granuloma process in mice lungs. Male C57BL/6 mice (N = 20) received intratracheal administration of silica particles (Silica; 20 mg in 50 μL saline) or saline (Control; 50 μL). After 15 days, the lung histology was performed through immunohistochemistry and morphometric analysis. Within silicotic granulomas, collagen V and FIZZ1 increased, while peroxisome proliferator-activated receptor gamma (PPARγ) positive cells decreased. In addition, the expression of proteins Notch-1, alpha smooth muscle actin (α-SMA) and macrophages163 (CD163) were higher in silicotic granulomas than control lungs. A significant positive correlation was found between collagen V and FIZZ1 (r = 0.70; p < 0.05), collagen V and Notch-1 (r = 0.72; p < 0.05), whereas Collagen V was inversely associated with peroxisome proliferator-activated receptor gamma (r=-0.69; p < 0.05). These findings suggested that collagen V association with FIZZ1, Notch-1 and PPARγ might be a key pathogenic mechanism for silicotic granulomas in mice lungs.

Pulmonary Silicosis Alters MicroRNA Expression in Rat Lung and miR-411-3p Exerts Anti-fibrotic Effects by Inhibiting MRTF-A/SRF Signaling

To identify potential therapeutic targets for pulmonary fibrosis induced by silica, we studied the effects of this disease on the expression of microRNAs (miRNAs) in the lung. Rattus norvegicus pulmonary silicosis models were used in conjunction with high-throughput screening of lung specimens to compare the expression of miRNAs in control and pulmonary silicosis tissues. A total of 70 miRNAs were found to be differentially expressed between control and pulmonary silicosis tissues. This included 41 miRNAs that were upregulated and 29 that were downregulated relative to controls. Among them, miR-292-5p, miR-155-3p, miR-1193-3p, miR-411-3p, miR-370-3p, and miR-409a-5p were found to be similarly altered in rat lung and transforming growth factor (TGF)-β1-induced cultured fibroblasts. Using miRNA mimics and inhibitors, we found that miR-1193-3p, miR-411-3p, and miR-370-3p exhibited potent anti-fibrotic effects, while miR-292-5p demonstrated pro-fibrotic effects in TGF-β1-stimulated lung fibroblasts. Moreover, we also found that miR-411-3p effectively reduced pulmonary silicosis in the mouse lung by regulating Mrtfa expression, as demonstrated using biochemical and histological assays. In conclusion, our findings indicate that miRNA expression is perturbed in pulmonary silicosis and suggest that therapeutic interventions targeting specific miRNAs might be effective in the treatment of this occupational disease.

Aluminum exposure promotes the metastatic proclivity of human colorectal cancer cells through matrix metalloproteinases and the TGF-β/Smad signaling pathway

Human exposure to aluminum (Al) mainly occurs through food intake. However, influences of Al on the gastrointestinal tract have been rarely reported. In particular, the effect of Al on the metastasis and angiogenesis of colorectal cancer cells has not been studied. Thus, we investigated the effect of Al on the metastatic proclivity using the human colorectal cancer cell line, HT-29. Cells were exposed to 1-16 mM AlCl₃ for 3-72 h. The effects of AlCl₃ on HT-29 cells for migration/invasion/adhesion, and metastasis-associated protein and gene expression were evaluated. AlCl₃ promoted cell migration and invasion, whereas it suppressed cell adhesion. AlCl₃-exposed cells showed decreased E-cadherin and increased vimentin and Snail. AlCl₃ increased transforming growth factor-beta (TGF-β) mRNA expression and Smad2/3 nuclear translocation. AlCl₃-treated cells had a higher mRNA expression of matrix metalloproteinase (MMP)-7 and -9 than the control. Particularly, AlCl₃-treated HT-29 cells promoted the angiogenesis of endothelial cells via increasing the secretion of vascular endothelial growth factor. Taken together, AlCl₃ can promote the metastatic proclivity of colorectal cancer cells through MMP-7, -9, and TGF-β/Smad2/3 pathway. Our data suggest that Al exposure of the gastrointestinal tract may be a risk factor for metastasis initiation in colorectal cancer cells.

Decreased Soluble Receptor of Advanced Glycation End Product Levels Correlated with Inflammation in Silicosis

Silicosis is a devastating disease caused by inhalation of silica dust that leads to inflammatory cascade and then scarring of the lung tissue. Increasing evidences indicate that soluble receptor for advanced glycation end products (sRAGE) is involved in inflammatory diseases. However, no data on the possible relationship between sRAGE and inflammation of silicosis are available. In this study, serum from subjects with silicosis (n = 59) or from healthy controls (HC, n = 14) was analyzed for the secretion of sRAGE, tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), transforming growth factor-β1 (TGF-β1), and oxidized low-density lipoprotein (ox-LDL). The associations between sRAGE and cytokines and ox-LDL and lung function were assessed by Pearson's correlation analyses. Mean levels of serum sRAGE were lower in silicosis than those in controls (p < 0.05). The subjects who had a longer term of occupational exposure had higher levels of sRAGE (p < 0.05). The secretion of TNF-α, IL-1β, IL-6, TGF-β1, and ox-LDL was significantly higher in the silicosis group than that in the HC group (p < 0.05). Furthermore, the levels of sRAGE were negatively correlated with TNF-α, IL-6, IL-1β, and ox-LDL. There is no correlation between sRAGE and TGF-β1 and lung function. The optimal point of sRAGE for differentiating silicosis from healthy controls was 14250.02 pg/ml by ROC curve analysis. A decrease in serum sRAGE and its association with inflammatory response might suggest a role for sRAGE in the pathogenesis of silicosis.

Inflammatory and oxidative stress biomarkers induced by silica exposure in crystal craftsmen

BACKGROUND

Identification of biomarkers associated with the diagnosis and prognosis of silicosis would be highly advantageous in the clinical setting. The aim of this study is to evaluate inflammatory and oxidative stress biomarkers in subjects exposed to silica.

METHODS

A cross-sectional study of crystal craftsmen currently (n = 34) or formerly (n = 35) exposed and a group of nonexposed subjects (n = 12) was performed. Personal respirable dust samples were collected. Plasma inflammatory mediators (bone morphogenetic protein- BMP2 and chemokines CXCL16, and CCL5), oxidative stress enzymes (thiobarbituric acid reactive substances [TBARs] and superoxide dismutase [SOD]), and nitrite (NO₂ ^- ) were analyzed in parallel with nitric oxide in exhaled breath (FeNO).

RESULTS

Being currently or formerly exposed to silica was related to increased levels of CXCL16 and TBARs. Currently, exposed subjects showed decreased levels of SOD. Thirty-seven craftsmen with silicosis (26 formerly and 11 currently exposed) showed higher levels of CXCL16, which was positively associated with the radiological severity of silicosis. Compared with the nonexposed, subjects with silicosis had higher levels of TBARs and those with complicated silicosis had lower levels of SOD. In multivariate analysis, higher levels of CXCL16 were associated with exposure status and radiological severity of silicosis. Smoking was not a confounder. FeNO did not distinguish between the exposure status and the presence of silicosis.

CONCLUSION

CXCL16 emerged as a potential biomarker that could distinguish both silica exposure and silicosis. TBARs were elevated in exposed individuals. However, their clinical applications demand further investigation in follow-up studies of representative samples.

Small and dangerous? Potential toxicity mechanisms of common exposure particles and nanoparticles

We are continuously exposed to large numbers of non-biological, persistent particulates through dermal, oral and inhalation routes. At sizes perfect for cell interactions, such modern particle exposures are derived from human engineering either purposefully (e.g. additives/excipients) or inadvertently (e.g. pollution). Whether oral or dermal exposure to common particles has significantly adverse effects is not yet known. However, relationships between increased morbidity or mortality and airborne particle exposure are well established. Large nanoparticles and microparticles adsorb environmental molecules, including antigens and allergens, and deliver them to cells potentially with an adjuvant effect. Smaller nanoparticles may have enhanced redox activity due to increased surface areas or band gap effects. Under some circumstances, ultrasmall nanoparticles can ligate cellular receptors or interact with other cell machinery and drive distinct cell signalling. These, as well as the potential for inflammasome activation, are discussed as feasible pathways to understanding or de-bunking particle toxicity.

Lupus, Silica, and Dietary Omega-3 Fatty Acid Interventions

Two environmental factors, crystalline silica (cSiO2), a toxic airborne particle encountered occupationally, and docosahexaenoic acid (DHA), a dietary omega-3 highly unsaturated fatty acid (HUFA), have the potential to influence the development of systemic lupus erythematosus (lupus). Using the NZBWF1 mouse, which spontaneously develops lupus, we found that intranasal exposure to cSiO2 significantly decreases latency and promotes rapid progression of the disease. Specifically, cSiO2 induces the development of ectopic lymphoid structures (ELS) containing germinal centers in the lungs that yield vigorous and diverse autoantibody responses locally and systemically. Transcriptomic analysis revealed that cSiO2 promotes a robust type I interferon gene signature that likely precipitates ELS neogenesis. Intriguingly, dietary supplementation with human-relevant doses of DHA impedes cSiO2-induced gene expression, ELS neogenesis, autoantibody elevation, and glomerulonephritis in this lupus-prone mouse model. Together, our findings point to the feasibility of enhancing tissue omega-3 HUFAs as a personalized nutritional intervention to impede onset and progression of environment-triggered autoimmune disease.

T Cell Dysregulation in Non-silicotic Silica Exposed Workers: A Step Toward Immune Tolerance Breakdown

Background: Chronic silica exposure can lead to silicosis, complicated or not by autoimmune diseases (AID). The pathophysiology of silica-induced AID remains not fully understood, especially immune mechanisms that may develop in patients without yet established silicosis. We conducted a prospective clinical study to analyze the impact of crystalline silica (CS) on T cell phenotype and regulatory T cells (Tregs) frequency, as well as on auto-antibodies development in non-silicotic workers exposed to CS.

Methods: Workers with moderate to high exposure level to CS and aged between 30 and 60 years-old were considered for inclusion. Peripheral blood mononuclear cells were analyzed by flow cytometry. Auto-antibodies were screened in serum by immunofluorescence. Blood from 42 and 45 healthy subjects (HC) was used as control for T cell phenotype and serum analyses, respectively.

Results: Among the 63 included workers exposed to CS, 55 had full data available and were analyzed. Ten were exposed to CS for <5 years, 18 for 5–10 years and 27 for more than 10 years. The frequency of Tregs (CD4⁺CD25⁺CD127⁻FoxP3⁺) was significantly lower in CS exposed workers as compared to HC. We found an increased expression of the activation marker HLA-DR on T cells (CD3⁺, CD4⁺, and CD8⁺) of CS exposed workers as compared to HC. Tregs to activated T cells ratio was also lower in exposed subjects. In the latter, HLA-DR expression level and Tregs frequency were significantly associated with CS exposure duration. Serum autoantibody detection was significantly higher in CS exposed workers as compared to HC. Especially, among workers exposed more than 10 years, antinuclear antibodies and ANCA were detected in 44 and 22% among them, as compared to 5 and 2.5% in HC, respectively.

Conclusion: This work shows that CS exposure is associated with a decrease of Tregs frequency, an increase of T cell activation status, and a tolerance breakdown against auto-antigens. These results show that alterations of the T cell compartment can be detected early over the course of CS exposure, preceding silicosis development or AID onset.

The CDR1as/miR-7/TGFBR2 Axis Modulates EMT in Silica-Induced Pulmonary Fibrosis

Silicosis is one of the typical forms of pneumoconiosis characterized by abnormal proliferation of fibroblasts and deposition of extracellular matrix. Recent findings have shown that microRNAs and circular RNAs (circRNAs) are implicated in many diseases. However, the function of noncoding RNAs in pulmonary fibrosis remain to be elucidated. Here, miR-7 was found significantly decreased in silica-treated pulmonary epithelial cells as well as in fibrotic lung tissues of mice. Elevated expression of miR-7 via agomir injection relieved lung fibrosis in vivo. Further molecular study showed that miR-7 played its role against pulmonary fibrosis by blocking epithelial-mesenchymal transition (EMT) progression of human bronchial epithelial cells and A549 cells. Notably, transforming growth factor beta receptor 2 (TGFBR2) was identified as a target gene of miR-7 with bioinformatics tools, which was verified by dual luciferase receptor gene assay in human bronchial epithelial cells and A549 cells. Silica induced elevation of TGFBR2 could be abolished by exogenous expression of miR-7. Furthermore, bioinformatics software indicated that circRNA CDR1as had several binding sites for miR-7. The inhibitory effects of miR-7 on EMT and its target TGFBR2 were suppressed by circRNA CDR1as, which contributed to pulmonary fibrosis. Our studies also revealed overexpressed miR-7 could repress fibrogenesis of lung fibroblasts induced by TGF-β1. Collectively, circRNA CDR1as stimulated by silica could sponge miR-7 to release TGFBR2, plays an important role during pulmonary fibrosis by promoting EMT process. These results indicated that the interaction between miR-7 and circRNA CDR1as may exert important functions and provide potential therapeutic targets in lung fibrotic diseases.