The puzzling issue of silica toxicity: are silanols bridging the gaps between surface states and pathogenicity?

A study of inflammatory biomarkers in crystalline silica exposed rock drillers

BACKGROUND

Crystalline silica (CS) exposure can cause serious lung disease in humans, but mechanisms of pulmonary toxicity have not been completely elucidated.

AIMS

To assess pro-inflammatory and anti-inflammatory biomarkers and biomarkers related to the development of chronic obstructive pulmonary disease and fibrosis in serum of rock drillers exposed to CS.

METHODS

Rock drillers (N = 123) exposed to CS and non-specified particulate matter (PM) were compared to 48 referents without current or past exposure to PM in a cross-sectional study.

RESULTS

The rock drillers had been exposed to CS for 10.7 years on average. Geometric mean (GM) current exposure was estimated to 36 µg/m3. Their GM concentration of matrix metalloproteinase 12 (MMP-12) was significantly higher (16 vs. 13 ng/L; p = 0.04), while interleukin (IL) 6 and IL-8 were significantly lower compared to the referents. Also pentraxin 3 was significantly lower (3558 vs. 4592 ng/L; p = 0.01) in the rock drillers. A dose-response relationship was observed between cumulative exposure to CS and MMP-12, the highest exposed subgroup having significantly higher MMP-12 concentrations than the referents.

CONCLUSION

Exposure to CS may increase circulating MMP-12 concentrations in a dose-response related fashion. The results may also suggest a down-regulation of pro-inflammatory pathways.

Targeting progranulin alleviated silica particles-induced pulmonary inflammation and fibrosis via decreasing Il-6 and Tgf-β1/Smad

Long term exposure to silica particles leads to various diseases, among which silicosis is of great concern. Silicosis is an interstitial lung disease caused by inhalation of silica particles in production environments. However, the mechanisms underlying silicosis remains unclear. Our previous studies revealed that progranulin (Pgrn) promoted the expression of pro-inflammatory factors in alveolar macrophages treated with silica particles and the secretion of extracellular matrix of pulmonary fibroblasts. Nevertheless, the role of Pgrn in silica particles-induced silicosis in vivo was unknown. This study found that silica particles increased Pgrn expression in silicosis patients. Pgrn deficiency reduced lung inflammation and fibrosis in silica particles-induced silicosis mouse models. Subsequently, based on transcriptional sequencing and interleukin (Il) -6 knockout mouse models, results demonstrated that Pgrn deficiency might decrease silicosis inflammation by reducing the production of Il-6, thereby modulating pulmonary fibrosis in the early stage of silicosis mouse models. Furthermore, another mechanism through which Pgrn deficiency reduced fibrosis in silicosis mouse models was the regulation of the transforming growth factor (Tgf) -β1/Smad signaling pathway. Conclusively, Pgrn contributed to silicosis inflammation and fibrosis induced by silica particles, indicating that Pgrn could be a promising therapeutic target.

Differential pulmonary toxicity and autoantibody formation in genetically distinct mouse strains following combined exposure to silica and diesel exhaust particles

BACKGROUND

Inhalation of airborne particulate matter, such as silica and diesel exhaust particles, poses serious long-term respiratory and systemic health risks. Silica exposure can lead to silicosis and systemic autoimmune diseases, while DEP exposure is linked to asthma and cancer. Combined exposure to silica and DEP, common in mining, may have more severe effects. This study investigates the separate and combined effects of occupational-level silica and ambient-level DEP on lung injury, inflammation, and autoantibody formation in two genetically distinct mouse strains, thereby aiming at understanding the interplay between genetic susceptibility, particulate exposure, and disease outcomes. Silica and diesel exhaust particles were administered to mice via oropharyngeal aspiration. Assessments of lung injury and host response included in vivo lung micro-computed tomography, lung function tests, bronchoalveolar lavage fluid analysis including inflammatory cytokines and antinuclear antibodies, and histopathology with particle colocalization.

RESULTS

The findings highlight the distinct effects of silica and diesel exhaust particles (DEP) on lung injury, inflammation, and autoantibody formation in C57BL/6J and NOD/ShiLtJ mice. Silica exposure elicited a well-established inflammatory response marked by inflammatory infiltrates, release of cytokines, and chemokines, alongside mild fibrosis, indicated by collagen deposition in the lungs of both C57BL/6J and NOD/ShilLtJ mice. Notably, these strains exhibited divergent responses in terms of respiratory function and lung volumes, as assessed through micro-computed tomography. Additionally, silica exposure induced airway hyperreactivity and elevated antinuclear antibody levels in bronchoalveolar lavage fluid, particularly prominent in NOD/ShiLtJ mice. Moreover, antinuclear antibodies correlated with extent of lung inflammation in NOD/ShiLTJ mice. Lung tissue analysis revealed DEP loaded macrophages and co-localization of silica and DEP particles. However, aside from contributing to airway hyperreactivity specifically in NOD/ShiLtJ mice, the ambient-level DEP did not significantly amplify the effects induced by silica. There was no evidence of synergistic or additive interaction between these specific doses of silica and DEP in inducing lung damage or inflammation in either of the mouse strains.

CONCLUSION

Mouse strain variations exerted a substantial influence on the development of silica induced lung alterations. Furthermore, the additional impact of ambient-level DEP on these silica-induced effects was minimal.

Paracrine signaling of ferroptotic airway epithelium in crystalline silica-induced pulmonary fibrosis augments local fibroblast activation through glycolysis reprogramming

Chronic exposure to crystalline silica (CS) contributes to pulmonary fibrosis. Airway epithelium dysfunction and fibroblast activation have both been recognized as pivotal players, alongside disturbances in ferroptosis and glycolysis reprogramming. However, the mechanisms involved remain unclear. In this study, we investigated the crosstalk between airway epithelium and fibroblast in the context of CS-induced pulmonary fibrosis. CS was employed in vivo and the in vitro co-culture system of airway epithelium and fibroblast. Spatial transcriptome analysis of CS-induced fibrotic lung tissue was conducted as well. Results showed that epithelium ferroptosis caused by CS enhanced TGFβ1-induced fibroblast activation through paracrine signaling. tPA was further identified to be the central mediator that bridges epithelium ferroptosis and fibroblast activation. And increased fibroblast glycolysis reprogramming was evidenced to promote fibroblast activation. By inhibition of epithelium ferroptosis or silencing tPA of airway epithelium, fibroblast AMPK phosphorylation was inhibited. Moreover, we revealed that tPA secreted by ferroptotic epithelium transmits paracrine signals to fibroblasts by governing glycolysis via p-AMPK/AMPK mediated Glut1 accumulation. Collectively, our study demonstrated the regulation of airway epithelium ferroptosis on fibroblast activation in CS-induced pulmonary fibrosis, which would shed light on the complex cellular crosstalk within pulmonary fibrosis and identify potential therapeutic targets.

Lysosomal BK channels facilitate silica-induced inflammation in macrophages

BACKGROUND

Lysosomal ion channels are proposed therapeutic targets for a number of diseases, including those driven by NLRP3 inflammasome-mediated inflammation. Here, the specific role of the lysosomal big conductance Ca2+-activated K+ (BK) channel was evaluated in a silica model of inflammation in murine macrophages. A specific-inhibitor of BK channel function, paxilline (PAX), and activators NS11021 and NS1619 were utilized to evaluate the role of lysosomal BK channel activity in silica-induced lysosomal membrane permeabilization (LMP) and NLRP3 inflammasome activation resulting in IL-1β release.

METHODS

Murine macrophages were exposed in vitro to crystalline silica following pretreatment with BK channel inhibitors or activators and LMP, cell death, and IL-1β release were assessed. In addition, the effect of PAX treatment on silica-induced cytosolic K+ decrease was measured. Finally, the effects of BK channel modifiers on lysosomal pH, proteolytic activity, and cholesterol transport were also evaluated.

RESULTS

PAX pretreatment significantly attenuated silica-induced cell death and IL-1β release. PAX caused an increase in lysosomal pH and decrease in lysosomal proteolytic activity. PAX also caused a significant accumulation of lysosomal cholesterol. BK channel activators NS11021 and NS1619 increased silica-induced cell death and IL-1β release. BK channel activation also caused a decrease in lysosomal pH and increase in lysosomal proteolytic function as well as a decrease in cholesterol accumulation.

CONCLUSION

Taken together, these results demonstrate that inhibiting lysosomal BK channel activity with PAX effectively reduced silica-induced cell death and IL-1β release. Blocking cytosolic K+ entry into the lysosome prevented LMP through the decrease of lysosomal acidification and proteolytic function and increase in lysosomal cholesterol.

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.

Differential Pulmonary Toxicity and Autoantibody Formation in Genetically Distinct Mouse Strains Following Combined Exposure to Silica and Diesel Exhaust Particles

Background

Inhalation of airborne particulate matter, such as silica and diesel exhaust particles, poses serious long-term respiratory health risks. Silica exposure can lead to silicosis and systemic autoimmune diseases, while DEP exposure is linked to asthma and cancer. Combined exposure to silica and DEP, common in mining, may have more severe effects. This study investigates the separate and combined effects of silica and DEP on lung injury, inflammation, and autoantibody formation in two genetically distinct mouse strains, thereby aiming at understanding the interplay between genetic susceptibility, particulate exposure, and disease outcomes. Silica and diesel exhaust particles were administered to mice via oropharyngeal aspiration. Assessments of lung injury and host response included in vivo lung micro-computed tomography, lung function tests, bronchoalveolar lavage fluid analysis including inflammatory cytokines and antinuclear antibodies, and histopathology with particle colocalization.

Results

Silica exposure elicited a well-established inflammatory response marked by inflammatory infiltrates, release of cytokines, and chemokines, alongside limited fibrosis, indicated by collagen deposition in the lungs of both C57BL/6J and NOD/ShilLtJ mice. Notably, these strains exhibited divergent responses in terms of respiratory function and lung volumes, as assessed through micro-computed tomography. Additionally, silica exposure induced airway hyperreactivity and elevated antinuclear antibody levels in bronchoalveolar lavage fluid, particularly prominent in NOD/ShiLtJ mice. Lung tissue analysis revealed DEP loaded macrophages and co-localization of silica and DEP particles.

Conclusion

Mouse strain variations exerted a substantial influence on the development of silica induced lung alterations. Furthermore, the additional impact of diesel exhaust particles on these silica-induced effects was minimal.

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.

Geochemical composition and potential health risks of geophagic materials: an example from a rural area in the Limpopo Province of South Africa

Geophagy is a common practice among rural population of the Fetakgomo Tubatse Local Municipality area in the Limpopo Province of South Africa. Although, the practice might be beneficial to the health of the consumers, its negative effects could overshadow the positive effects and might lead to detrimental health issues. The present work sought to investigate the geochemical composition as well as pH and organic matter (OM) content of geophagic materials commonly consumed in the study area. Furthermore, assessment of the potential health risk of the materials on geophagic individuals was also considered. Twelve samples were collected in the study area and analysed by X-ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for major and trace elements composition. The results showed higher concentrations of non-essential elements (e.g., As, Cr, Pb) than the proposed recommended daily standards intake, suggesting a potential health risk. The alkaline nature (pH 6.80 to 9.22) of the studied samples might affect the bioacessibility of some essential elements. Furthermore, the OM content (> 0.7%) observed in some of the studied samples may retain pathogenic micro-organisms detrimental to health. Although As and Cr presented a low bioaccessible fraction (< 16.0%), health risk assessment revealed that their concentrations represented a hazard (HQ > 1) and might induce non-carcinogenic health threats to geophagic individuals. Based on the geochemical analysis, pH and OM content as well as health risk assessment findings, the studied geophagic materials are not considered suitable for human consumption. The practice should therefore be discouraged amongst the population in the study area to avoid possible detrimental health issues.

Physico-Chemical Approaches to Investigate Surface Hydroxyls as Determinants of Molecular Initiating Events in Oxide Particle Toxicity

The study of molecular recognition patterns is crucial for understanding the interactions between inorganic (nano)particles and biomolecules. In this review we focus on hydroxyls (OH) exposed at the surface of oxide particles (OxPs) which can play a key role in molecular initiating events leading to OxPs toxicity. We discuss here the main analytical methods available to characterize surface OH from a quantitative and qualitative point of view, covering thermogravimetry, titration, ζ potential measurements, and spectroscopic approaches (NMR, XPS). The importance of modelling techniques (MD, DFT) for an atomistic description of the interactions between membranes/proteins and OxPs surfaces is also discussed. From this background, we distilled a new approach methodology (NAM) based on the combination of IR spectroscopy and bioanalytical assays to investigate the molecular interactions of OxPs with biomolecules and membranes. This NAM has been already successfully applied to SiO₂ particles to identify the OH patterns responsible for the OxPs' toxicity and can be conceivably extended to other surface-hydroxylated oxides.

Workers with Suspected Diagnosis of Silicosis: A Case Study of Sarcoidosis Versus Siderosis

Silicosis is one of the most important occupational respiratory diseases worldwide, hence the importance of making a correct diagnosis. Diagnosis is commonly based on radiological findings according to the ILO International Classification of Radiographs of Pneumoconioses and occupational exposure. High-resolution computed tomography is indicated for differential diagnosis. This article presents two cases with an initial diagnosis of silicosis that ended up being diagnosed as sarcoidosis and siderosis, respectively. The first case was a 42-year-old male who worked as a crushing operator in an underground copper and molybdenum mine for 22 years. He had a history of exposure to silicon dioxide and was asymptomatic. X-rays did not distinguish silicosis or siderosis, but histological findings (open lung biopsy) allowed for a diagnosis of sarcoidosis. The second case was a 50-year-old male who had worked as a welder in a molybdenum filter plant, an open pit mine since 2013; he spent the previous 20 years as a welder in an underground copper mine, with exposure to silicon dioxide and was symptomatic. The first radiograph showed opacities that were compatible with pulmonary silicosis. A subsequent high-resolution computed tomography and lung biopsy showed a pattern of pulmonary siderosis. Due to the similarities in the radiographs of these three diseases, greater emphasis must be placed on the differential diagnosis, for which a complete occupational and clinical history is important in order to provide clues for the performance of complementary tests to avoid misdiagnosing.

Mesoporous Silica Nanoparticles as a Gene Delivery Platform for Cancer Therapy

Cancer remains a major global health challenge. Traditional chemotherapy often results in side effects and drug resistance, necessitating the development of alternative treatment strategies such as gene therapy. Mesoporous silica nanoparticles (MSNs) offer many advantages as a gene delivery carrier, including high loading capacity, controlled drug release, and easy surface functionalization. MSNs are biodegradable and biocompatible, making them promising candidates for drug delivery applications. Recent studies demonstrating the use of MSNs for the delivery of therapeutic nucleic acids to cancer cells have been reviewed, along with their potential as a tool for cancer therapy. The major challenges and future interventions of MSNs as gene delivery carriers for cancer therapy are discussed.

Crystalline silica-induced macrophage pyroptosis interacting with mitophagy contributes to pulmonary fibrosis via modulating mitochondria homeostasis

Environmental exposure to crystalline silica (CS) can lead to silicosis. Alveolar macrophages (AMs) play a crucial role in the pathogenesis of silicosis. Previously, we demonstrated that enhancing AMs mitophagy exerted protective effects on silicosis with a restrained inflammatory response. However, the exact molecular mechanisms are elusive. Pyroptosis and mitophagy are two different biological processes that determine cell fate. Exploring whether there were interactions or balances between these two processes in AMs would provide new insight into treating silicosis. Here we reported that crystalline silica induced pyroptosis in silicotic lungs and AMs with apparent mitochondria injury. Notably, we identified a reciprocal inhibitory effect between mitophagy and pyroptosis cascades in AMs. By enhancing or diminishing mitophagy, we demonstrated that PINK1-mediated mitophagy helped clear damaged mitochondria to negatively regulate CS-induced pyroptosis. While constraining pyroptosis cascades by NLRP3, Caspase1, and GSDMD inhibitors, respectively, displayed enhanced PINK1-dependent mitophagy with lessened CS-injured mitochondria. These observed effects were echoed in the mice with enhanced mitophagy. Therapeutically, we demonstrated abolishing GSDMD-dependent pyroptosis by disulfiram attenuated CS-induced silicosis. Collectively, our data demonstrated that macrophage pyroptosis interacting with mitophagy contributes to pulmonary fibrosis via modulating mitochondria homeostasis, which may provide potential therapeutic targets.

Human dendritic cell maturation induced by amorphous silica nanoparticles is Syk-dependent and triggered by lipid raft aggregation

BACKGROUND

Synthetic amorphous silica nanoparticles (SAS-NPs) are widely employed in pharmaceutics, cosmetics, food and concretes. Workers and the general population are exposed daily via diverse routes of exposure. SAS-NPs are generally recognized as safe (GRAS) by the Food and Drug Administration, but because of their nanoscale size and extensive uses, a better assessment of their immunotoxicity is required. In the presence of immune "danger signals", dendritic cells (DCs) undergo a maturation process resulting in their migration to regional lymph nodes where they activate naive T-cells. We have previously shown that fumed silica pyrogenic SAS-NPs promote the two first steps of the adaptative immune response by triggering DC maturation and T-lymphocyte response, suggesting that SAS-NPs could behave as immune "danger signals". The present work aims to identify the mechanism and the signalling pathways involved in DC phenotype modifications provoked by pyrogenic SAS-NPs. As a pivotal intracellular signalling molecule whose phosphorylation is associated with DC maturation, we hypothesized that Spleen tyrosine kinase (Syk) may play a central role in SAS-NPs-induced DC response.

RESULTS

In human monocyte-derived dendritic cells (moDCs) exposed to SAS-NPs, Syk inhibition prevented the induction of CD83 and CD86 marker expression. A significant decrease in T-cell proliferation and IFN-γ, IL-17F and IL-9 production was found in an allogeneic moDC:T-cell co-culture model. These results suggested that the activation of Syk was necessary for optimal co-stimulation of T-cells. Moreover, Syk phosphorylation, observed 30 min after SAS-NP exposure, occurred upstream of the c-Jun N-terminal kinase (JNK) Mitogen-activated protein kinases (MAPK) and was elicited by the Src family of protein tyrosine kinases. Our results also showed for the first time that SAS-NPs provoked aggregation of lipid rafts in moDCs and that MβCD-mediated raft destabilisation altered Syk activation.

CONCLUSIONS

We showed that SAS-NPs could act as an immune danger signal in DCs through a Syk-dependent pathway. Our findings revealed an original mechanism whereby the interaction of SAS-NPs with DC membranes promoted aggregation of lipid rafts, leading to a Src kinase-initiated activation loop triggering Syk activation and functional DC maturation.

Neutralization of interleukin-11 attenuates silica particles-induced pulmonary inflammation and fibrosis in vivo

Environmental exposure to crystalline silica particles can lead to silicosis, which is one of the most serious pulmonary interstitial fibrosis around the world. Unfortunately, the exact mechanism on silicosis is unclear, and the effective treatments are lacking to date. In this study, we aim to explore the molecular mechanism by which interleukin-11 (IL-11) affects silica particles-induced lung inflammation and fibrosis. We observed that IL-11 expressions in mouse lungs were significantly increased after silica exposure, and maintained at high levels across both inflammation and fibrosis phase. Immunofluorescent dual staining further revealed that the overexpression of IL-11 mainly located in mouse lung epithelial cells and fibroblasts. Using neutralizing anti-IL-11 antibody could effectively alleviate the overexpression of pro-inflammatory cytokines (i.e., interleukin-6 and tumor necrosis factor-α) and fibrotic proteins (i.e., collagen type I and matrix metalloproteinase-2) induced by silica particles. Most importantly, the expressions of IL-11 receptor subunit α (IL-11Rα), Glycoprotein 130 (GP130), and phosphorylated extracellular signal-regulated kinase (p-ERK) were significantly increased in response to silica, whereas blocking of IL-11 markedly reduced their levels. All findings suggested that the overexpression of IL-11 was involved in the pathological of silicosis, while neutralizing IL-11 antibody could effectively alleviate the silica-induced lung inflammation and fibrosis by inhibiting the IL-11Rα/GP130/ERK signaling pathway. IL-11 might be a promising therapeutic target for lung inflammation and fibrosis caused by silica particles exposure.

Stimuli-Responsive Silica Silanol Conjugates: Strategic Nanoarchitectonics in Targeted Drug Delivery

The design of novel drug delivery systems is exceptionally critical in disease treatments. Among the existing drug delivery systems, mesoporous silica nanoparticles (MSNs) have shown profuse promise owing to their structural stability, tunable morphologies/sizes, and ability to load different payload chemistry. Significantly, the presence of surface silanol groups enables functionalization with relevant drugs, imaging, and targeting agents, promoting their utility and popularity among researchers. Stimuli-responsive silanol conjugates have been developed as a novel, more effective way to conjugate, deliver, and release therapeutic drugs on demand and precisely to the selected location. Therefore, it is urgent to summarize the current understanding and the surface silanols' role in making MSN a versatile drug delivery platform. This review provides an analytical understanding of the surface silanols, chemistry, identification methods, and their property-performance correlation. The chemistry involved in converting surface silanols to a stimuli-responsive silica delivery system by endogenous/exogenous stimuli, including pH, redox potential, temperature, and hypoxia, is discussed in depth. Different chemistries for converting surface silanols to stimuli-responsive bonds are discussed in the context of drug delivery. The critical discussion is culminated by outlining the challenges in identifying silanols' role and overcoming the limitations in synthesizing stimuli-responsive mesoporous silica-based drug delivery systems.

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.

Tuning Mesoporous Silica Nanoparticles in Novel Avenues of Cancer Therapy

The global menace of cancer has led to an increased death toll in recent years. The constant evolution of cancer therapeutics with novel delivery systems has paved the way for translation of innovative therapeutics from bench to bedside. This review explains the significance of mesoporous silica nanoparticles (MSNs) as delivery vehicles with particular emphasis on cancer therapy, including novel opportunities for biomimetic therapeutics and vaccine delivery. Parameters governing MSN synthesis, therapeutic agent loading characteristics, along with tuning of MSN toward cancer cell specificity have been explained. The advent of MSN in nanotheranostics and its potential in forming nanocomposites for imaging purposes have been illustrated. Additionally, various hurdles encountered during the bench to bedside translation have been explained along with potential avenues to circumvent them. This also opens up new horizons in drug delivery, which could be useful to researchers in the years to come.

Building the uracil skeleton in primitive ponds at the origins of life: carbamoylation of aspartic acid

A large set of nucleobases and amino acids is found in meteorites, implying that several chemical reservoirs are present in the solar system. The "geochemical continuity" hypothesis explores how protometabolic paths developed from so-called "bricks" in an enzyme-free prebiotic world and how they affected the origins of life. In the living cell, the second step of synthesizing uridine and cytidine RNA monomers is a carbamoyl transfer from a carbamoyl donor to aspartic acid. Here we compare two enzyme-free scenarios: aqueous and mineral surface scenarios in a thermal range up to 250 °C. Both processes could have happened in ponds under open atmosphere on the primeval Earth. Carbamoylation of aspartic acid with cyanate in aqueous solutions at 25 °C gives high N-carbamoyl aspartic acid yields within 16 h. It is important to stress that, while various molecules could be efficient carbamoylating agents according to thermodynamics, kinetics plays a determining role in selecting prebiotically possible pathways.

Differential immunological effects of silica nanoparticles on peripheral blood mononuclear cells of silicosis patients and controls

Silicosis is a fibrotic disease caused by the inhalation of respirable silica particles, which are typically engulfed by alveolar macrophages and subsequently induce the release of inflammatory cytokines. Various animal experimental and human studies have focused on modeling silicosis, to assess the interactions of macrophages and other cell types with silica particles. There is still, however, limited knowledge on the differential response upon silica-exposure between silicosis patients and controls. We focused on studying the responsiveness of peripheral blood mononuclear cells (PBMCs) to silica nanoparticles (SiNPs) - Ludox and NM-200 - of silicosis patients and controls. The proliferative capacity of T- CD3⁺ and B- CD19⁺ cells, were evaluated via Carboxyfluorescein succinimidyl ester (CFSE) assay. The activation status of lymphocyte subsets and response to silica were also evaluated by comparing the extent of micro-granuloma or aggregate formation with the cytokine secretion profiles between both groups of individuals. The proliferative capacity of CD19⁺ cells was elevated in silicotic patients as opposed to controls. Subsets of regulatory T cells (CD4⁺ CD25⁺ and CD8⁺ CD25⁺) and immunoglobulins IgM and IgG were also significantly increased in patients. The number and the size of aggregates formed were higher with SiNPs stimulation in patients compared to controls. Multivariable analysis also elucidated the role of key cytokines like interleukin-1β (IL-1β), IL-6 and interferon-gamma (IFN-γ), which were upregulated in SiNP-stimulated PBMCs of patients compared to controls. Our ex vivo model thus has potential to provide insights into the immunological effects of silica particles in lymphocytes of silicosis patients and controls.

Understanding the pathogenesis of occupational coal and silica dust-associated lung disease

Workers in the mining and construction industries are at increased risk of respiratory and other diseases as a result of being exposed to harmful levels of airborne particulate matter (PM) for extended periods of time. While clear links have been established between PM exposure and the development of occupational lung disease, the mechanisms are still poorly understood. A greater understanding of how exposures to different levels and types of PM encountered in mining and construction workplaces affect pathophysiological processes in the airways and lungs and result in different forms of occupational lung disease is urgently required. Such information is needed to inform safe exposure limits and monitoring guidelines for different types of PM and development of biomarkers for earlier disease diagnosis. Suspended particles with a 50% cut-off aerodynamic diameter of 10 µm and 2.5 µm are considered biologically active owing to their ability to bypass the upper respiratory tract's defences and penetrate deep into the lung parenchyma, where they induce potentially irreversible damage, impair lung function and reduce the quality of life. Here we review the current understanding of occupational respiratory diseases, including coal worker pneumoconiosis and silicosis, and how PM exposure may affect pathophysiological responses in the airways and lungs. We also highlight the use of experimental models for better understanding these mechanisms of pathogenesis. We outline the urgency for revised dust control strategies, and the need for evidence-based identification of safe level exposures using clinical and experimental studies to better protect workers' health.

Molecular recognition between membrane epitopes and nearly free surface silanols explains silica membranolytic activity

Inhaled crystalline silica causes inflammatory lung diseases, but the mechanism for its unique activity compared to other oxides remains unclear, preventing the development of potential therapeutics. Here, the molecular recognition mechanism between membrane epitopes and "nearly free silanols" (NFS), a specific subgroup of surface silanols, is identified and proposed as a novel broad explanation for particle toxicity in general. Silica samples having different bulk and surface properties, specifically different amounts of NFS, are tested with a set of membrane systems of decreasing molecular complexity and different charge. The results demonstrate that NFS content is the primary determinant of membrane disruption causing red blood cell lysis and changes in lipid order in zwitterionic, but not in negatively charged liposomes. NFS-rich silica strongly and irreversibly adsorbs zwitterionic self-assembled phospholipid structures. This selective interaction is corroborated by density functional theory and supports the hypothesis that NFS recognize membrane epitopes that exhibit a positive quaternary amino and negative phosphate group. These new findings define a new paradigm for deciphering particle-biomembrane interactions that will support safer design of materials and what types of treatments might interrupt particle-biomembrane interactions.

Magnesium for Implants: A Review on the Effect of Alloying Elements on Biocompatibility and Properties

An attempt is made to cover the whole of the topic of biodegradable magnesium (Mg) alloys with a focus on the biocompatibility of the individual alloying elements, as well as shed light on the degradation characteristics, microstructure, and mechanical properties of most binary alloys. Some of the various work processes carried out by researchers to achieve the alloys and their surface modifications have been highlighted. Additionally, a brief look into the literature on magnesium composites as also been included towards the end, to provide a more complete picture of the topic. In most cases, the chronological order of events has not been particularly followed, and instead, this work is concentrated on compiling and presenting an update of the work carried out on the topic of biodegradable magnesium alloys from the recent literature available to us.

Eryptosis is an indicator of hematotoxicity in the risk assessment of environmental amorphous silica nanoparticles exposure: The role of macromolecule corona

Silica nanoparticles (SiO₂ NPs) have been widely manufactured for various applications and unintentionally generated in various industrial processes. SiO₂ NPs exposure is potentially hazardous to human health. Incremental evidence has indicated the presence of SiO₂ NPs in systemic circulation, which warranted their interaction with blood components. Due to the obvious weakness of hemolysis in the risk assessment of environmental NPs, we for the first time use eryptosis as a sensitive indicator to assess the hematotoxicity of SiO₂ NPs. In vitro results showed that the exposure of erythrocytes to pristine SiO₂ NPs resulted in typical features of eryptosis, including oxidative stress, calcium influx, phosphatidylserine externalization and hemolysis. However, SiO₂ NPs covered with mouse plasma (SiO₂@MP) or grafted with polyvinylpyrrolidone (SiO₂@PVP) did not stimulate eryptosis. Interestingly, neither bare nor macromolecule-decolorated SiO₂ NPs caused eryptosis in our in vivo mouse model, highlighting the protective role of coronal proteins on the amelioration of SiO₂ NPs-induced hematotoxicity. These results emphasized the influences of surface modification on the toxicity of environmental NPs.

Pulmonary Toxicity of Silica Linked to Its Micro- or Nanometric Particle Size and Crystal Structure: A Review

Silicon dioxide (SiO2) is a mineral compound present in the Earth’s crust in two mineral forms: crystalline and amorphous. Based on epidemiological and/or biological evidence, the pulmonary effects of crystalline silica are considered well understood, with the development of silicosis, emphysema, chronic bronchitis, or chronic obstructive pulmonary disease. The structure and capacity to trigger oxidative stress are recognized as relevant determinants in crystalline silica’s toxicity. In contrast, natural amorphous silica was long considered nontoxic, and was often used as a negative control in experimental studies. However, as manufactured amorphous silica nanoparticles (or nanosilica or SiNP) are becoming widely used in industrial applications, these paradigms must now be reconsidered at the nanoscale (<100 nm). Indeed, recent experimental studies appear to point towards significant toxicity of manufactured amorphous silica nanoparticles similar to that of micrometric crystalline silica. In this article, we present an extensive review of the nontumoral pulmonary effects of silica based on in vitro and in vivo experimental studies. The findings of this review are presented both for micro- and nanoscale particles, but also based on the crystalline structure of the silica particles.

Surface Treatment With Hydrophobic Coating Reagents (Organosilanes) Strongly Reduces the Bioactivity of Synthetic Amorphous Silica in vitro

Synthetic amorphous silica (SAS) is industrially relevant material whose bioactivity in vitro is strongly diminished, for example, by protein binding to the particle surface. Here, we investigated the in vitro bioactivity of fourteen SAS (pyrogenic, precipitated, or colloidal), nine of which were surface-treated with organosilanes, using alveolar macrophages as a highly sensitive test system. Dispersion of the hydrophobic SAS required pre-wetting with ethanol and extensive ultrasonic treatment in the presence of 0.05% BSA (Protocol 1). Hydrophilic SAS was suspended by moderate ultrasonic treatment (Protocol 2) and also by Protocol 1. The suspensions were administered to NR8383 alveolar macrophages under serum-free conditions for 16 h, and the release of LDH, GLU, H2O2, and TNFα was measured in cell culture supernatants. While seven surface-treated hydrophobic SAS exhibited virtually no bioactivity, two materials (AEROSIL® R 504 and AEROSIL® R 816) had minimal effects on NR8383 cells. In contrast, non-treated SAS elicited considerable increases in LDH, GLU, and TNFα, while the release of H2O2 was low except for CAB-O-SIL® S17D Fumed Silica. Dispersing hydrophilic SAS with Protocol 1 gradually reduced the bioactivity but did not abolish it. The results show that hydrophobic coating reagents, which bind covalently to the SAS surface, abrogate the bioactivity of SAS even under serum-free in vitro conditions. The results may have implications for the hazard assessment of hydrophobic surface-treated SAS in the lung.

Dissolution Rate of Nanomaterials Determined by Ions and Particle Size under Lysosomal Conditions: Contributions to Standardization of Simulant Fluids and Analytical Methods

Dissolution of inhaled engineered nanomaterials (ENM) under physiological conditions is essential to predict the clearance of the ENM from the lungs and to assess their biodurability and the potential effects of released ions. Alveolar macrophage (AM) lysosomes contain a pH 4.5 saline brine with enzymes and other components. Different types of artificial phagolysosomal simulant fluids (PSFs) have been developed for dissolution testing, but the consequence of using different media is not known. In this study, we tested to which extent six fundamentally different PSFs affected the ENM dissolution kinetics and particle size as determined by a validated transmission electron microscopy (TEM) image analysis. Three lysosomal simulant media were consistent with each other and with in vivo clearance. These media predict the quick dissolution of ZnO, the partial dissolution of SiO2, and the very slow dissolution of TiO2. The valid media use either a mix of organic acids (with the total concentration below 0.5 g/L, thereof citric acid below 0.15 g/L) or another organic acid (KH phthalate). For several ENM, including ZnO, BaSO4, and CeO2, all these differences induce only minor modulation of the dissolution rates. Only for TiO2 and SiO2, the interaction with specific organic acids is highly sensitive, probably due to sequestration of the ions, and can lead to wrong predictions when compared to the in vivo behavior. The media that fail on TiO2 and SiO2 dissolution use citric acid at concentrations above 5 g/L (up to 28 g/L). In the present selection of ENM, fluids, and methods, the different lysosomal simulant fluids did not induce changes of particle morphology, except for small changes in SiO2 and BaSO4 particles most likely due to ion dissolution, reprecipitation, and coalescence between neighboring particles. Based on the current evidence, the particle size by TEM analysis is not a sufficiently sensitive analytical method to deduce the rate of ENM dissolution in physiological media. In summary, we recommend the standardization of ENM dissolution testing by one of the three valid lysosomal simulant fluids with determination of the dissolution rate and halftime by the quantification of ions. This recommendation was established for a continuous flow system but may be relevant as well for static (batch) solubility testing.

Comparing α-Quartz-Induced Cytotoxicity and Interleukin-8 Release in Pulmonary Mono- and Co-Cultures Exposed under Submerged and Air-Liquid Interface Conditions

The occupational exposure to particles such as crystalline quartz and its impact on the respiratory tract have been studied extensively in recent years. For hazard assessment, the development of physiologically more relevant in-vitro models, i.e., air-liquid interface (ALI) cell cultures, has greatly progressed. Within this study, pulmonary culture models employing A549 and differentiated THP-1 cells as mono-and co-cultures were investigated. The different cultures were exposed to α-quartz particles (Min-U-Sil5) with doses ranging from 15 to 66 µg/cm² under submerged and ALI conditions and cytotoxicity as well as cytokine release were analyzed. No cytotoxicity was observed after ALI exposure. Contrarily, Min-U-Sil5 was cytotoxic at the highest dose in both submerged mono- and co-cultures. A concentration-dependent release of interleukin-8 was shown for both exposure types, which was overall stronger in co-cultures. Our findings showed considerable differences in the toxicological responses between ALI and submerged exposure and between mono- and co-cultures. A substantial influence of the presence or absence of serum in cell culture media was noted as well. Within this study, the submerged culture was revealed to be more sensitive. This shows the importance of considering different culture and exposure models and highlights the relevance of communication between different cell types for toxicological investigations.

The High-Throughput In Vitro CometChip Assay for the Analysis of Metal Oxide Nanomaterial Induced DNA Damage

Metal oxide nanomaterials (MONMs) are among the most highly utilized classes of nanomaterials worldwide, though their potential to induce DNA damage in living organisms is known. High-throughput in vitro assays have the potential to greatly expedite analysis and understanding of MONM induced toxicity while minimizing the overall use of animals. In this study, the high-throughput CometChip assay was used to assess the in vitro genotoxic potential of pristine copper oxide (CuO), zinc oxide (ZnO), and titanium dioxide (TiO2) MONMs and microparticles (MPs), as well as five coated/surface-modified TiO2 NPs and zinc (II) chloride (ZnCl2) and copper (II) chloride (CuCl2) after 2–4 h of exposure. The CuO NPs, ZnO NPs and MPs, and ZnCl2 exposures induced dose- and time-dependent increases in DNA damage at both timepoints. TiO2 NPs surface coated with silica or silica–alumina and one pristine TiO2 NP of rutile crystal structure also induced subtle dose-dependent DNA damage. Concentration modelling at both post-exposure timepoints highlighted the contribution of the dissolved species to the response of ZnO, and the role of the nanoparticle fraction for CuO mediated genotoxicity, showing the differential impact that particle and dissolved fractions can have on genotoxicity induced by MONMs. The results imply that solubility alone may be insufficient to explain the biological behaviour of MONMs.

Rapid Assessment of Oxidative Damage Potential: A Comparative Study of Engineered Stone Dusts Using a Deoxyguanosine Assay

The popularity of engineered stone (ES) has been associated with a global increase in occupational lung disease in workers exposed to respirable dust during the fabrication of benchtops and other ES products. In this study, the reactivity and subsequent oxidative reduction potential of freshly generated ES dusts were evaluated by (i) comparing different engineered and natural stones, (ii) comparing settled and respirable stone dust fractions and (iii) assessing the effect of ageing on the reactivity of freshly generated stone dust. An established cell-free deoxyguanosine hydroxylation assay was used to assess the potential for oxidative DNA damage. ES dust exhibited a higher relative reactivity than two of the three natural stones tested. Respirable dust fractions were found to be significantly more reactive than their corresponding settled fraction (ANOVA, p < 0.05) across all stone types and samples. However, settled dust still displayed high relative reactivity. The lower reactivity of the settled dust was not due to decay in reactivity of the respirable dust when it settled but rather a result of the admixture of larger nonrespirable particles. No significant change in respirable dust reactivity was observed for three ES samples over a 21-day time period, whereas a significant decrease in reactivity was observed in the natural stone studied. This study has practical implications for dust control and housekeeping in industry, risk assessment and hazard management.

Characterisation of dust emissions from machined engineered stones to understand the hazard for accelerated silicosis

Engineered stones are novel construction materials associated with a recent upsurge in silicosis cases among workers in the stonemason industry. In order to understand the hazard for the short latency of lung disease among stonemasons, we simulated real-time dust exposure scenario by dry-machining engineered stones in controlled conditions, capturing and analysing the respirable dust generated for physical and chemical characteristics. Natural granite and marble were included for comparison. Cutting engineered stones generated high concentrations of very fine particles (< 1 µm) with > 80% respirable crystalline silica content, in the form of quartz and cristobalite. Engineered stones also contained 8–20% resin and 1–8% by weight metal elements. In comparison, natural stones had far lower respirable crystalline silica (4- 30%) and much higher metal content, 29–37%. Natural stone dust emissions also had a smaller surface area than engineered stone, as well as lower surface charge. This study highlighted the physical and chemical variability within engineered stone types as well as between engineered and natural stones. This information will ultimately help understand the unique hazard posed by engineered stone fabrication work and help guide the development of specific engineering control measures targeting lower exposure to respirable crystalline silica.

Exposure to silicates and systemic autoimmune-related outcomes in rodents: a systematic review

BACKGROUND

Autoimmunity can result from the interplay between genetic background and effects of environmental and/or occupational exposure to hazardous materials. Several compounds, including silica dust, have been linked with systemic autoimmunity and systemic autoimmune diseases, based on epidemiological evidence. For asbestos, a strong link with systemic autoimmune diseases does not yet exist, however, several studies have documented features of autoimmunity following asbestos exposure. Even so, human studies are limited in their ability to identify and examine isolated exposures, making it difficult to demonstrate causation or to assess pathogenic mechanisms. Therefore, this systematic review examines the existing animal evidence regarding autoimmunity and exposure to silicates (silica and asbestos).

METHODS

PubMed and EMBASE were systematically searched for peer-reviewed studies examining systemic autoimmune disease-related outcomes after silicate exposure in rodents. Literature databases were searched up to September 2021 for studies written in English and where the full text was available. Search strings were established based on a PECO (Population, Exposure, Comparator, Outcome) format. After title, abstract, and full-text screening, thirty-four studies were identified for further analysis. Quality assessment through ToxR tool and qualitative analysis of the results was performed.

RESULTS

Although there was significant heterogeneity in the included studies in terms of exposure protocol and genetic background of the rodent models used, it was noted that both genetic background and exposure to silicates [(crystalline) silica and asbestos] are highly relevant to the development of (sub-) clinical systemic autoimmune disease.

CONCLUSION

Parallels were observed between the findings from the animal (this review) and human (epidemiological) studies, arguing that experimental animal models are valuable tools for examining exacerbation or development of autoimmune disease after silicate exposure. However, genetic background and synergism between exposures should be considered in future studies.

Role of scavenger receptors in silica nanoparticle-induced cytokine responses in bronchial epithelial cells

A major challenge in nanoparticle (NP) research is to elucidate how NPs activate initial targets in cells, leading to cytotoxicity and inflammation. We have previously shown that silica (Si)NPs induce pro-inflammatory responses in bronchial epithelial cells (BEAS-2B) via mechanisms involving transforming growth factor (TGF)-α release, and activation of MAP-kinase p38 and JNK besides NF-κB (p65). In the present study, the roles of scavenger receptors (SRs) in SiNP-induced cytokine responses in BEAS-2B cells were examined by siRNA silencing. Cells exposed to Si10 and Si50 (nominal sizes 10 and 50 nm) showed marked interleukin (IL)-6, CXCL8, IL-1α, IL-1β responses. Transient knockdown of SR-B1, LOX-1 and CXCL16 reduced the Si10- and Si50-induced cytokine responses, to a different magnitude dependent on the particle size, SR and cytokine. Si10-induced TGF-α responses were also markedly reduced by knockdown of SR-B1 and CXCL16. Furthermore, the role of SR-B1 in Si10-induced phosphorylations of p65 and MAP-kinases p38 and JNK were examined, and no significant reductions were observed upon knockdown of SR-B1. In conclusion, LOX-1 and CXCL16 and especially SR-B1 seem to have important roles in mediating cytokine responses and TGF-α release due to SiNP exposure in BEAS-2B cells, without a down-stream role of MAP-kinase and NF-κB.

Synthetic amorphous silica nanoparticles promote human dendritic cell maturation and CD4 + T-lymphocyte activation

Innate immune cells such as dendritic cells (DCs) sense and engulf nanomaterials potentially leading to an adverse immune response. Indeed, as described for combustion-derived particles, nanomaterials could be sensed as danger signals, enabling DCs to undergo a maturation process, migrate to regional lymph nodes and activate naive T-lymphocytes. Synthetic amorphous silica nanoparticles (SAS-NPs) are widely used as food additives, cosmetics, and construction materials. This work aimed to evaluate in vitro the effects of manufactured SAS-NPs, produced by thermal or wet routes, on human DCs functions and T-cell activation. Human monocyte-derived DCs (moDCs) were exposed for 16 hours to three endotoxin-free test materials: fumed silica NPs from Sigma-Aldrich (#S5505) or the JRC Nanomaterial Repository (NM-202) and colloidal Ludox®TMA NPs. Cell viability, phenotypical changes, cytokines production, internalization, and allogeneic CD4+ T-cells proliferation were evaluated. Our results showed that all SAS-NPs significantly upregulated the surface expression of CD86 and CD83 activation markers. Secretions of pro-inflammatory cytokines (CXCL-8 and CXCL-12) were significantly enhanced in a dose-dependent manner in the moDCs culture supernatants by all SAS-NPs tested. In an allogeneic co-culture, fumed silica-activated moDCs significantly increased T-lymphocyte proliferation at all T-cell:DC ratios compared to unloaded moDCs. Moreover, analysis of co-culture supernatants regarding the production of T-cell-derived cytokines showed a significant increase of IL-9 and IL-17A and F, as well as an upregulation of IL-5, consistent with the pro-inflammatory phenotype of treated-moDCs. Taken together, these results suggest that SAS-NPs could induce functional moDCs maturation and play a role in the immunization process against environmental antigens.

Analyzing the surface of functional nanomaterials-how to quantify the total and derivatizable number of functional groups and ligands

Functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are of increasing relevance for many key technologies of the twenty-first century. This includes polymer and silica or silica-coated nanoparticles (NP) with covalently bound surface groups, semiconductor quantum dots (QD), metal and metal oxide NP, and lanthanide-based NP with coordinatively or electrostatically bound ligands, as well as surface-coated nanostructures like micellar encapsulated NP. The surface chemistry can significantly affect the physicochemical properties of NM, their charge, their processability and performance, as well as their impact on human health and the environment. Thus, analytical methods for the characterization of NM surface chemistry regarding chemical identification, quantification, and accessibility of functional groups (FG) and surface ligands bearing such FG are of increasing importance for quality control of NM synthesis up to nanosafety. Here, we provide an overview of analytical methods for FG analysis and quantification with special emphasis on bioanalytically relevant FG broadly utilized for the covalent attachment of biomolecules like proteins, peptides, and oligonucleotides and address method- and material-related challenges and limitations. Analytical techniques reviewed include electrochemical titration methods, optical assays, nuclear magnetic resonance and vibrational spectroscopy, as well as X-ray based and thermal analysis methods, covering the last 5-10 years. Criteria for method classification and evaluation include the need for a signal-generating label, provision of either the total or derivatizable number of FG, need for expensive instrumentation, and suitability for process and production control during NM synthesis and functionalization.

The emerging role of inorganic elements as potential antigens in sarcoidosis

PURPOSE OF REVIEW

Previous studies mainly described a role for organic agents as possible triggers for sarcoidosis. In this review, we address recent studies suggesting a possible role for inorganic elements, such as metals or silica in sarcoidosis pathogenesis.

RECENT FINDINGS

Several epidemiological papers suggest that inorganic agents, either by environmental exposures or occupational activities, could trigger sarcoidosis. Association between inorganics and sarcoidosis is also described in several recently published case reports and studies demonstrating immunological sensitization to inorganic agents in sarcoidosis patients.Studies comparing chronic beryllium disease (CBD) and sarcoidosis suggest that although antigenic triggers may differ, underlying processes may be comparable.Besides the fact that a growing number of studies show a possible role for inorganic triggers, it is also suggested that inorganic triggered sarcoidosis may result in a more severe phenotype, including pulmonary fibrosis.

SUMMARY

We can use the knowledge already gained on CBD pathogenesis to conduct further research into role of inorganics, such as metals and silica as antigens in sarcoidosis. Given the importance of a lymphocyte proliferation test (LPT) in diagnosing CBD, it seems obvious to also implement this test in the diagnostic work-up of sarcoidosis to identify patients with an inorganic antigenic trigger of their disease.

Interactive toxicity effect of combined exposure to hematite and amorphous silicon dioxide nanoparticles in human A549 cell line

The study on the health effects of combined exposure to various contaminants has been recommended by many authors. The objective of the present study was to examine the effects of the co-exposure to hematite and amorphous silicon dioxide (A-SiO₂) nanoparticles on the human lung A₅₄₉ cell line. The A₅₄₉ cell line was exposed to 10, 50, 100, and 250 µg/ml concentrations of hematite and A-SiO₂ nanoparticles both independently and in combination. Their toxicity in both circumstances was investigated by MTT, intracellular reactive oxygen species, cell glutathione content, and mitochondrial membrane potential tests, and the type of interaction was investigated by statistical analysis using Statistical Package for Social Sciences (SPSS, v. 21). Results showed that the independent exposure to either hematite or A-SiO₂ compared with the control group produced more toxic effects on the A₅₄₉ cell line. The toxicity of combined exposure of the nanoparticles was lower compared with independent exposure, and antagonistic interactive effects were detected. The findings of this study could be useful in clarifying the present debate on the health effects of combined exposure of hematite and A-SiO₂ nanoparticles. Because of the complexities of combined exposures, further studies of this kind are recommended.

Mesoporous Silica Nanoparticles: Properties and Strategies for Enhancing Clinical Effect

Due to the theragnostic potential of mesoporous silica nanoparticles (MSNs), these were extensively investigated as a novel approach to improve clinical outcomes. Boasting an impressive array of formulations and modifications, MSNs demonstrate significant in vivo efficacy when used to identify or treat myriad malignant diseases in preclinical models. As MSNs continue transitioning into clinical trials, a thorough understanding of the characteristics of effective MSNs is necessary. This review highlights recent discoveries and advances in MSN understanding and technology. Specific focus is given to cancer theragnostic approaches using MSNs. Characteristics of MSNs such as size, shape, and surface properties are discussed in relation to effective nanomedicine practice and projected clinical efficacy. Additionally, tumor-targeting options used with MSNs are presented with extensive discussion on active-targeting molecules. Methods for decreasing MSN toxicity, improving site-specific delivery, and controlling release of loaded molecules are further explained. Challenges facing the field and translation to clinical environments are presented alongside potential avenues for continuing investigations.

The role of macrophage-derived TGF-β1 on SiO2-induced pulmonary fibrosis: A review

Silicosis is an occupational fibrotic lung disease caused by inhaling large amounts of crystalline silica dust. Transforming growth factor-β1 (TGF-β1), which is secreted from macrophages, has an important role in the development of this disease. Macrophages can recognize and capture silicon dust, undergo M2 polarization, synthesize TGF-β1 precursors, and secrete them out of the cell where they are activated. Activated TGF-β1 induces cells from different sources, transforming them into myofibroblasts through autocrine and paracrine mechanisms, ultimately causing silicosis. These processes involve complex molecular events, which are not yet fully understood. This systematic summary may further elucidate the location and development of pulmonary fibrosis in the formation of silicosis. In this review, we discussed the proposed cellular and molecular mechanisms of production, secretion, activation of TGF-β1, as well as the mechanisms through which TGF-β1 induces cells from three different sources into myofibroblasts during the pathogenesis of silicosis. This study furthers the medical understanding of the pathogenesis and theoretical basis for diagnosing silicosis, thereby promoting silicosis prevention and treatment.

Bridging the gap between toxicity and carcinogenicity of mineral fibres by connecting the fibre crystal-chemical and physical parameters to the key characteristics of cancer

Airborne fibres and particularly asbestos represent hazards of great concern for human health because exposure to these peculiar particulates may cause malignancies such as lung cancer and mesothelioma. Currently, many researchers worldwide are focussed on fully understanding the patho-biological mechanisms leading to carcinogenesis prompted by pathogenic fibres. Along this line, the present work introduces a novel approach to correlate how and to what extent the physical/crystal-chemical and morphological parameters (including length, chemistry, biodurability, and surface properties) of mineral fibres cause major adverse effects with an emphasis on asbestos. The model described below conceptually attempts to bridge the gap between toxicity and carcinogenicity of mineral fibres and has several implications: 1) it provides a tool to measure the toxicity and pathogenic potential of asbestos minerals, allowing a quantitative rank of the different types (e.g. chrysotile vs. crocidolite); 2) it can predict the toxicity and pathogenicity of "unregulated" or unclassified fibres; 3) it reveals the parameters of a mineral fibre that are active in stimulating key characteristics of cancer, thus offering a strategy for developing specific cancer prevention strategies and therapies. Chrysotile, crocidolite and fibrous glaucophane are described here as mineral fibres of interest.

Macrophage Autophagy and Silicosis: Current Perspective and Latest Insights

Silicosis is an urgent public health problem in many countries. Alveolar macrophage (AM) plays an important role in silicosis progression. Autophagy is a balanced mechanism for regulating the cycle of synthesis and degradation of cellular components. Our previous study has shown that silica engulfment results in lysosomal rupture, which may lead to the accumulation of autophagosomes in AMs of human silicosis. The excessive accumulation of autophagosomes may lead to apoptosis in AMs. Herein, we addressed some assumptions concerning the complex function of autophagy-related proteins on the silicosis pathogenesis. We also recapped the molecular mechanism of several critical proteins targeting macrophage autophagy in the process of silicosis fibrosis. Furthermore, we summarized several exogenous chemicals that may cause an aggravation or alleviation for silica-induced pulmonary fibrosis by regulating AM autophagy. For example, lipopolysaccharides or nicotine may have a detrimental effect combined together with silica dust via exacerbating the blockade of AM autophagic degradation. Simultaneously, some natural product ingredients such as atractylenolide III, dioscin, or trehalose may be the potential AM autophagy regulators, protecting against silicosis fibrosis. In conclusion, the deeper molecular mechanism of these autophagy targets should be explored in order to provide feasible clues for silicosis therapy in the clinical setting.

In vitro cytotoxicity study of superparamagnetic iron oxide and silica nanoparticles on pneumocyte organelles

Inhalation is the main route of nanoparticles (NP) exposure during manufacturing. Although many mechanisms of toxicity have been described, the interaction of NP with relevant pneumocytes organelles is not widely understood. Considering that the physicochemical properties of NP influence their toxicological responses, the objective of this study was to evaluate whether exposure to different NP, crystalline Fe₃O₄ NP and amorphous SiO₂ NP could alter pneumocytes organelles in alveolar epithelial cells. To achieve this goal, cell viability, ultrastructural changes, lysosomal damage, mitochondrial membrane potential (MMP), lipid droplets (LD) formation and cytokines production were evaluated by MTT, electron microscopy, lysotracker red staining, JC-1, Oil Red staining and Milliplex® assay respectively. Both NP were observed within lamellar bodies (LB), lysosomes, and cytoplasm causing morphological changes. Exposure to SiO₂ NP at 6 h induced lysosomal activation, but not Fe₃O₄ NP. MMP decreased and LD increased at the highest concentrations after both NP exposure. Pro-inflammatory cytokines were released only after SiO₂ NP exposure at 48 h. These results indicate that SiO₂ NP have a greater impact than Fe₃O₄ NP on organelles responsible for energy, secretion, degradation and metabolism in pneumocytes leading to the development of respiratory disorders or the exacerbation of preexisting conditions. Therefore, the established biocompatibility for amorphous NP has to be reconsidered.

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.

Mineralogy, geochemistry and toxicity of size-segregated respirable deposited dust in underground coal mines

We focus on a comparison of the geochemistry and mineralogy patterns found in coal, deposited dust (DD), respirable deposited dust (RDD) and inhalable suspended dust (PM10) from a number of underground mines located in China, with an emphasis on potential occupational health relevance. After obtaining the RDD from DD, a toxicological analysis (oxidative potential, OP) was carried out and compared with their geochemical patterns. The results demonstrate: i) a dependence of RDD/DD on the moisture content for high rank coals that does not exist for low rank coals; ii) RDD enrichment in a number of minerals and/or elements related to the parent coal, the wear on mining machinery, lime gunited walls and acid mine drainage; and iii) the geochemical patterns of RDD obtained from DD can be compared with PM10 with relatively good agreement, demonstrating that the characterization of DD and RDD can be used as a proxy to help evaluate the geochemical patterns of suspended PM10. With regards to the toxicological properties of RDD, the Fe content and other by-products of pyrite oxidation, as well as that of anatase, along with Si, Mn and Ba, and particle size (among others), were highly correlated with Ascorbic Acid and/or Glutathione OP.

Nearly free surface silanols are the critical molecular moieties that initiate the toxicity of silica particles

Inhalation of silica particles can induce inflammatory lung reactions that lead to silicosis and/or lung cancer when the particles are biopersistent. This toxic activity of silica dusts is extremely variable depending on their source and preparation methods. The exact molecular moiety that explains and predicts this variable toxicity of silica remains elusive. Here, we have identified a unique subfamily of silanols as the major determinant of silica particle toxicity. This population of "nearly free silanols" (NFS) appears on the surface of quartz particles upon fracture and can be modulated by thermal treatments. Density functional theory calculations indicates that NFS locate at an intersilanol distance of 4.00 to 6.00 Å and form weak mutual interactions. Thus, NFS could act as an energetically favorable moiety at the surface of silica for establishing interactions with cell membrane components to initiate toxicity. With ad hoc prepared model quartz particles enriched or depleted in NFS, we demonstrate that NFS drive toxicity, including membranolysis, in vitro proinflammatory activity, and lung inflammation. The toxic activity of NFS is confirmed with pyrogenic and vitreous amorphous silica particles, and industrial quartz samples with noncontrolled surfaces. Our results identify the missing key molecular moieties of the silica surface that initiate interactions with cell membranes, leading to pathological outcomes. NFS may explain other important interfacial processes involving silica particles.

Pulmonary surfactant inhibition of nanoparticle uptake by alveolar epithelial cells

Pulmonary surfactant forms a sub-micrometer thick fluid layer that covers the surface of alveolar lumen and inhaled nanoparticles therefore come in to contact with surfactant prior to any interaction with epithelial cells. We investigate the role of the surfactant as a protective physical barrier by modeling the interactions using silica-Curosurf-alveolar epithelial cell system in vitro. Electron microscopy displays that the vesicles are preserved in the presence of nanoparticles while nanoparticle-lipid interaction leads to formation of mixed aggregates. Fluorescence microscopy reveals that the surfactant decreases the uptake of nanoparticles by up to two orders of magnitude in two models of alveolar epithelial cells, A549 and NCI-H441, irrespective of immersed culture on glass or air-liquid interface culture on transwell. Confocal microscopy corroborates the results by showing nanoparticle-lipid colocalization interacting with the cells. Our work thus supports the idea that pulmonary surfactant plays a protective role against inhaled nanoparticles. The effect of surfactant should therefore be considered in predictive assessment of nanoparticle toxicity or drug nanocarrier uptake. Models based on the one presented in this work may be used for preclinical tests with engineered nanoparticles.

Silica-related diseases in the modern world

Silicosis is an ancient and potentially fatal pneumoconiosis caused by exposure to respirable crystalline silica. Silicosis is historically a disease of miners; however, failure to recognize and control the risk associated with silica exposure in contemporary work practices such as sandblasting denim jeans and manufacturing of artificial stone benchtops has led to re-emergence of silicosis around the world. This review outlines the mineralogy, epidemiology, clinical and radiological features of the various forms of silicosis and other silica-associated diseases. Perspective is provided on the most recent studies shedding light on pathogenesis, including the central role of innate immune effector cells and subsequent inflammatory cascades in propagating pulmonary fibrosis and the extrapulmonary manifestations, which uniquely characterize this pneumoconiosis. Clinical conundrums in differential diagnosis, particularly between silicosis and sarcoidosis, are highlighted, as is the importance of obtaining a careful occupational history in the patient presenting with pulmonary infiltrates and/or fibrosis. While silicosis is a completely preventable disease, unfortunately workers around the world continue to be affected and experience progressive or even fatal disease. Although no treatments have been proven, opportunities to intervene to prevent progressive disease, founded in a thorough cellular and molecular understanding of the immunopathology of silicosis, are highlighted.

A Human-Relevant 3D In Vitro Platform for an Effective and Rapid Simulation of Workplace Exposure to Nanoparticles: Silica Nanoparticles as Case Study

In this contribution, we show the suitability of a 3D airway model, when coupled with a nebulizer system, for simulating workplace exposure to nanoparticles. As a proof of concept, workplace exposure to silica nanoparticles was experimentally measured in an occupational facility where nanoparticles are produced weekly, and compared with the official limit value for bulk silica materials. These values of potential exposure were simulated in a 3D airway model by nebulizing low doses (from 0.90 to 55 µg/cm2) of silica nanoparticles over a prolonged period (12 weeks of repeated exposure, 5 days per week). Overall, the results suggest the efficiency of the defense mechanisms of the respiratory system and the clearance of the breathed silica nanoparticles by the mucociliary apparatus in accordance with the recent in vivo data. This in vitro platform shows that the doses tested may correlate with the occupational exposure limit values. Such relationship could provide regulatory-oriented data useful for risk classification of nanomaterials.

Amino Functionalized Micro-Mesoporous Hybrid Particles for the Sustained Release of the Antiretroviral Drug Tenofovir

The sustained release of an antiretroviral agent to women mucosa has been proved as an excellent strategy to reduce the sexual transmission of HIV. Hybrid micro-mesoporous particles have been synthesized and functionalized with a silane coupling agent followed by loading the antiretroviral tenofovir. It has been observed that the disposition of the silane molecule on the surface of the particles determines the interaction mechanism with the antiretroviral molecule loaded independently on the surface area of the particles. In this sense, available and free amino groups are required to achieve a smart pH-responsive material, a condition that is only achieved in those materials containing a silane chemisorbed monolayer. Moreover, the modulation of the release kinetics attributed to the presence of the silane monolayer covering the mesopores has been confirmed by fitting the releasing curves to the first order and Weibull models. The developed micro-mesoporous particles have been demonstrated to be excellent smart-release vehicles for antiviral agents and can be safely used in polymer mucoadhesive vaginal gels.