Comparison of nanoparticle exposures between fumed and sol-gel nano-silica manufacturing facilities

Determination of the Nanoscale Silica Mass Fraction by AF4/ICP-MS with Isotope Dilution Analysis Using 29Si-Enriched Silica Nanoparticles

A methodology based on the use of asymmetrical flow field-flow fractionation (AF4) coupled to ICP-MS with size fraction-targeted isotope dilution analysis (IDA) has been developed, validated, and applied for the first time to determine the mass fraction of nanoscale silica (SiO2). For this purpose, 29Si-enriched SiO2 nanoparticles, to be used as an IDA spike/internal standard, were synthesized and characterized in-house. Double IDA was used to quantify an aqueous suspension of Stöber silica particles of similar characteristics to those of the 29SiO2 nanoparticle (NP) spike using a representative test material of natural Si isotopic composition as the calibrant. For fumed SiO2 NP in a highly complex food matrix, a methodology based on single IDA with AF4/ICP-MS using the same 29SiO2 NP spike was developed and validated. Relative expanded measurement uncertainties (k = 2) of 4% (double IDA) and 8% (single IDA) were achieved for nanoscale silica mass fractions of 5143 and 107 mg kg-1 in water suspension and food matrix, respectively. To assess the accuracy of AF4/ICP-IDMS for the characterization of SiO2 NP in a food matrix, standard addition measurements on samples spiked with Aerosil AF200, also in-house characterized for Si mass fraction, were undertaken, with an average recovery of 95.6 ± 4.1% (RSD, n = 3) obtained. The particle-specific IDA data obtained for both SiO2 NP-containing samples were also compared with that of post-AF4 channel external calibration using inorganic Si standards. The mass fractions obtained by IDA agreed well with those obtained by external calibration within their associated measurement uncertainties.

Advances in the study of silica nanoparticles in lung diseases

Silicon dioxide nanoparticles (SiNPs) are one of the major forms of silicon dioxide and are composed of the most-abundant compounds on earth. Based on their excellent properties, SiNPs are widely used in food production, synthetic processes, medical diagnostics, drug delivery, and other fields. The mass production and wide application of SiNPs increases the risk of human exposure to SiNPs. In the workplace and environment, SiNPs mainly enter the human body through the respiratory tract and reach the lungs; therefore, the lungs are the most important and most toxicologically affected target organ of SiNPs. An increasing number of studies have shown that SiNP exposure can cause severe lung toxicity. However, studies on the toxicity of SiNPs in ex vivo and in vivo settings are still in the exploratory phase. The molecular mechanisms underlying the lung toxicity of SiNPs are varied and not yet fully understood. As a result, this review summarizes the possible mechanisms of SiNP-induced lung toxicity, such as oxidative stress, endoplasmic reticulum stress, mitochondrial damage, and cell death. Moreover, this study provides a summary of the progression of diseases caused by SiNPs, thereby establishing a theoretical basis for future studies on the mechanisms of SiNP-induced lung toxicity.

Prospects and hazards of silica nanoparticles: Biological impacts and implicated mechanisms

With the thrive of nanotechnology, silica nanoparticles (SiNPs) have been extensively adopted in the agriculture, food, cosmetic, and even biomedical industries. Due to the mass production and use, SiNPs inevitably entered the environment, resulting in ecological toxicity and even posing a threat to human health. Although considerable investigations have been conducted to assess the toxicity of SiNPs, the correlation between SiNPs exposure and consequent health risks remains ambiguous. Since the biological impacts of SiNPs can differ from their design and application, the toxicity assessment for SiNPs may be extremely difficult. This review discussed the application of SiNPs in different fields, especially their biomedical use, and documented their potential release pathways into the environment. Meanwhile, the current process of assessing SiNPs-related toxicity on various model organisms and cell lines was also detailed, thus estimating the health threats posed by SiNPs exposure. Finally, the potential toxic mechanisms of SiNPs were also elaborated based on results obtained from both in vivo and in vitro trials. This review generally summarizes the biological effects of SiNPs, which will build up a comprehensive perspective of the application and toxicity of SiNPs.

Silicon dioxide nanoparticles compromise decidualization via autophagy impairment to possibly cause embryo resorption

The wide application of silicon dioxide nanoparticles (SiO₂NPs) has raised concerns about their harmful effects on reproduction. The purpose of this research was to investigate the toxic effects and the possible mechanisms by which SiO₂NPs affect decidualization and pregnancy progression. We found that SiO₂NPs could inhibit decidualization, both in mice and in human endometrial stromal cells (HESCs). Embryo resorption was also evident in mice treated with SiO₂NPs. When HESCs were treated with SiO₂NPs, decidualization was inhibited and there was an increase in intracellular lysosomes and autophagosomes as well as the blockage of autophagic flux. Interestingly, a reduction of autophagosome accumulation via 3-methyladenine (3MA) significantly restored the decidualization of HESCs. In summary, our results indicate that SiO₂NPs can affect embryo survival by impairing decidualization through a dysfunctional autophagic process.

Silica nanoparticles induce cardiac injury and dysfunction via ROS/Ca2+/CaMKII signaling

Interest is growing to better comprehend the interaction of silica nanoparticles (SiNPs) with the cardiovascular system. In particular, the extremely small size, relatively large surface area and associated unique properties may greatly enhance its toxic potentials compared to larger-sized counterparts. Nevertheless, the underlying mechanisms still need to be evaluated. In this context, the cardiotoxicity of nano-scale (Si-60; particle diameter about 60 nm) and submicro-scale silica particles (Si-300; 300 nm) were examined in ApoE^-/- mice via intratracheal instillation, 6.0 mg/kg·bw, once per week for 12 times. The echocardiography showed that the sub-chronic exposure of Si-60 declined cardiac output (CO) and stroke volume (SV), shorten LVIDd and LVIDs, and thickened LVAWs of ApoE^-/- mice in compared to the control and Si-300 groups. Histological investigations manifested Si-60 enhanced inflammatory infiltration, myocardial fiber arrangement disorder, hypertrophy and fibrosis in the cardiac tissue, as well as mitochondrial ultrastructural injury. Accordingly, the serum cTnT, cTnI and ANP were significantly elevated by Si-60, as well as cardiac ANP content. In particular, Si-60 greatly increased cardiac ROS, Ca²⁺ levels and CaMKII activation in comparison with Si-300. Further, in vitro investigations revealed silica particles induced a dose- and size-dependent activation of oxidative stress, mitochondrial membrane permeabilization, intracellular Ca²⁺ overload, CaMKII signaling activation and ensuing myocardial apoptosis in human cardiomyocytes (AC16). Mechanistic analyses revealed SiNPs induced myocardial apoptosis via ROS/Ca²⁺/CaMKII signaling, which may contribute to the abnormalities in cardiac structure and function in vivo. In summary, our research revealed SiNPs caused myocardial impairments, dysfunction and even structural remodeling via ROS/Ca²⁺/CaMKII signaling. Of note, a size-dependent myocardial toxicity was noticed, that is, Si-60 greater than Si-300.

Amorphous silica nanoparticles caused lung injury through the induction of epithelial apoptosis via ROS/Ca2+/DRP1-mediated mitochondrial fission signaling

The adverse effects of amorphous silica nanoparticles (SiNPs) exposure on the respiratory system were increasingly recognized, however, its potential pathogenesis still remains not fully elucidated. So, this study aimed to explore its effects on pulmonary injury, and to investigate related mechanisms. Histological investigations illustrated SiNPs triggered the lung injury, mainly manifested as alveolar structure destruction, collagen deposition, and mitochondrial ultrastructural injury. In particular, SiNPs greatly enhanced pulmonary ROS and TUNEL positive rate in lungs, both of which were positively correlated with lung impairments. Further, the underlying mechanisms were investigated in cultured human bronchial epithelial cells (16HBE). Consistent with the in vivo findings, SiNPs caused the impairments on mitochondrial structure, as well as the activation of ROS generation and oxidative injury. Upon SiNPs stimuli, mitochondrial respiration was greatly inhibited, while Ca2+ overload in cytosol and mitochondria owing to ER calcium release was noticed, resulting in mitochondrial-dependent epithelial apoptosis. More importantly, mitochondrial dynamics was imbalanced toward a fission type, as evidenced by upregulated DRP1 and its phosphorylation at Ser616 (DRP1s616), while downregulated DRP1s637, and also MFN1, MFN2. Mechanistic investigations revealed that the activation of ROS/Ca2+ signaling promoted DRP1-mediated mitochondrial fission by SiNPs, forming a vicious cycle, and ultimately contributing to apoptosis in 16HBE. In summary, our results disclosed SiNPs caused pulmonary injury through the induction of epithelial apoptosis via a ROS/Ca2+/DRP1-mediated mitochondrial fission axis.

Toxic Impacts of Amorphous Silica Nanoparticles on Liver and Kidney of Male Adult Rats: an In Vivo Study

The toxic effects of the amorphous silica nanoparticles have not been thoroughly studied. Moreover, the majority of the in vivo investigations were performed using an inhalation exposure method. The current study aimed to explore the potential toxic effects of silica nanoparticles (SiNPs) after the treatment of adult male rats with two different concentrations (500 and 1000 ppm) via drinking water for 28 days. The genotoxicity, antioxidant status, and liver and kidney functions were assessed. Besides, histopathological and immunohistochemical evaluations were performed. The results showed a significant elevation in the malondialdehyde (MDA) level concurrent with a reduction in total reduced glutathione (GSH) concentration and catalase activity in the 1000-ppm SiNP-exposed rats as well as increase in ALT and AST activity confirmed by various histopathological alterations detected in liver. Also, in the 1000-ppm SiNP-exposed animals, there was an elevation in urea and creatinine levels confirmed by histopathological alterations detected in kidneys. Immunohistochemical findings in both liver and kidneys indicated strong expression of caspase-3 in the 1000-ppm SiNP-treated rats compared with the control and 500-ppm SiNP-treated groups. Such findings indicated that the 1000-ppm SiNPs exerted severe hepato-renal toxic impacts when compared with the control and 500-ppm SiNP-exposed rats.

Oxidative stress- and mitochondrial dysfunction-mediated cytotoxicity by silica nanoparticle in lung epithelial cells from metabolomic perspective

Quantities of researches have demonstrated silica nanoparticles (SiNPs) exposure inevitably induced damage to respiratory system, nonetheless, knowledge of its toxicological behavior and metabolic interactions with the cellular machinery that determines the potentially deleterious outcomes are limited and poorly elucidated. Here, the metabolic responses of lung bronchial epithelial cells (BEAS-2B) under SiNPs exposure were investigated using ultra performance liquid chromatography-mass spectrum (UPLC-MS)-based metabolomics research. Results revealed that even with low cytotoxicity, SiNPs disturbed global metabolism. Five metabolic pathways were significantly perturbed, in particular, oxidative stress- and mitochondrial dysfunction-related GSH metabolism and pantothenate and coenzyme A (CoA) biosynthesis, where the identified metabolites glutathione (GSH), glycine, beta-alanine, cysteine, cysteinyl-glycine and pantothenic acid were included. In support of the metabolomics profiling, SiNPs caused abnormality in mitochondrial structure and mitochondrial dysfunction, as evidenced by the inhibition of cellular respiration and ATP production. Moreover, SiNPs triggered oxidative stress as confirmed by the dose-dependent ROS generation, down-regulated nuclear factor erythroid 2-related factor 2 (NRF2) signaling, together with GSH depletion in SiNPs-treated BEAS-2B cells. Oxidative DNA damage and cell membrane dis-integrity were also detected in response to SiNPs exposure, which was correspondingly in agreed with the elevated 8-hydroxyguanosine (8-OHdG) and decreased phospholipids screened through metabolic analysis. Thereby, we successfully used the metabolomics approaches to manifest SiNPs-elicited toxicity through oxidative stress, mitochondrial dysfunction, DNA damage and rupture of membrane integrity in BEAS-2B cells. Overall, our study provided novel insights into the mechanism underlying SiNPs-induced pulmonary toxicity.

Assessment of Occupational Exposure to Indium Dust for Indium-Tin-Oxide Manufacturing Workers

According to recent research, indium nanoparticles (NPs) are more toxic than micro-sized particles. While cases of indium lung disease have been reported worldwide, very little research has been conducted on the occupational exposure to indium NPs. Recently, an indium-related lung disease was reported in Korea, a global powerhouse for display manufacturing. In this study, we conducted an assessment ofoccupational exposure at an indium tin oxide (ITO) powder manufacturing plant, where the first case of indium lung disease in Korea occurred. Airborne dustwas obtained from a worker's breathing zone, and area sampling in the workplace environment was conducted using real-time monitoring devices. Personal samples were analyzed for the indium concentrations in total dust, respirable dust fraction, and NPs using personal NPs respiratory deposition samplers. The total indium concentration of the personal samples was lower than the threshold limit value recommended by the American Conference of Governmental Industrial Hygienists (ACGIH TLV), which was set as occupational exposure limit (OEL). However, the respirable indium concentration exceeded the recently set ACGIH TLV for the respirable fraction of indium dust. The concentration of indium NPs ranged between 0.003 and 0.010 × 10-2 mg/m3, accounting for only 0.4% of the total and 2.7% of the respirable indium particles. This was attributed to the aggregating of NPs at the µm sub-level. Given the extremely low fraction of indium NPs in the total and respirable dust, the current OEL values, set as the total and respirable indium concentrations, do not holistically represent the occupational exposure to indium NPs or prevent health hazards. Therefore, it is necessary to set separate OEL values for indium NPs. This study covers only the process of handling ITO powder. Therefore, follow-up studies need to be conducted on other ITO sputtering target polishing and milling processes, which typically generate more airborne NPs, to further investigate the effects of indium on workers and facilitate the necessary implementation of indium-reducing technologies.

Signaling Pathways Regulated by Silica Nanoparticles

Silica nanoparticles are a class of molecules commonly used in drug or gene delivery systems that either facilitate the delivery of therapeutics to specific drug targets or enable the efficient delivery of constructed gene products into biological systems. Some in vivo or in vitro studies have demonstrated the toxic effects of silica nanoparticles. Despite the availability of risk management tools in response to the growing use of synthetic silica in commercial products, the molecular mechanism of toxicity induced by silica nanoparticles is not well characterized. The purpose of this study was to elucidate the effects of silica nanoparticle exposure in three types of cells including human aortic endothelial cells, mouse-derived macrophages, and A549 non-small cell lung cancer cells using toxicogenomic analysis. The results indicated that among all three cell types, the TNF and MAPK signaling pathways were the common pathways upregulated by silica nanoparticles. These findings may provide insight into the effects of silica nanoparticle exposure in the human body and the possible mechanism of toxicity.

Amorphous silica nanoparticles accelerated atherosclerotic lesion progression in ApoE-/- mice through endoplasmic reticulum stress-mediated CD36 up-regulation in macrophage

Background

The biosafety concern of silica nanoparticles (SiNPs) is rapidly expanding alongside with its mass production and extensive applications. The cardiovascular effects of SiNPs exposure have been gradually confirmed, however, the interaction between SiNPs exposure and atherosclerosis, and the underlying mechanisms still remain unknown. Thereby, this study aimed to explore the effects of SiNPs on the progression of atherosclerosis, and to investigate related mechanisms.

Results

We firstly investigated the in vivo effects of SiNPs exposure on atherosclerosis via intratracheal instillation of ApoE^−/− mice fed a Western diet. Ultrasound microscopy showed a significant increase of pulse wave velocity (PWV) compared to the control group, and the histopathological investigation reflected a greater plaque burden in the aortic root of SiNPs-exposed ApoE^−/− mice. Compared to the control group, the serum levels of total triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C) were elevated after SiNPs exposure. Moreover, intensified macrophage infiltration and endoplasmic reticulum (ER) stress was occurred in plaques after SiNPs exposure, as evidenced by the upregulated CD68 and CHOP expressions. Further in vitro, SiNPs was confirmed to activate ER stress and induce lipid accumulation in mouse macrophage, RAW264.7. Mechanistic analyses showed that 4-PBA (a classic ER stress inhibitor) pretreatment greatly alleviated SiNPs-induced macrophage lipid accumulation, and reversed the elevated CD36 expression induced by SiNPs.

Conclusions

Our results firstly revealed the acceleratory effect of SiNPs on the progression of atherosclerosis in ApoE^−/− mice, which was related to lipid accumulation caused by ER stress-mediated upregulation of CD36 expression in macrophage.

Graphical abstract

Toxicity to RAW264.7 Macrophages of Silica Nanoparticles and the E551 Food Additive, in Combination with Genotoxic Agents

Synthetic amorphous silica (SAS) is used in a plethora of applications and included in many daily products to which humans are exposed via inhalation, ingestion, or skin contact. This poses the question of their potential toxicity, particularly towards macrophages, which show specific sensitivity to this material. SAS represents an ideal candidate for the adsorption of environmental contaminants due to its large surface area and could consequently modulate their toxicity. In this study, we assessed the toxicity towards macrophages and intestinal epithelial cells of three SAS particles, either isolated SiO₂ nanoparticles (LS30) or SiO₂ particles composed of agglomerated-aggregates of fused primary particles, either food-grade (E551) or non-food-grade (Fumed silica). These particles were applied to cells either alone or in combination with genotoxic co-contaminants, i.e., benzo[a]pyrene (B[a]P) and methane methylsulfonate (MMS). We show that macrophages are much more sensitive to these toxic agents than a non-differenciated co-culture of Caco-2 and HT29-MTX cells, used here as a model of intestinal epithelium. Co-exposure to SiO₂ and MMS causes DNA damage in a synergistic way, which is not explained by the modulation of DNA repair protein mRNA expression. Together, this suggests that SiO₂ particles could adsorb genotoxic agents on their surface and, consequently, increase their DNA damaging potential.

Microarray-assisted size-effect study of amorphous silica nanoparticles on human bronchial epithelial cells

Amorphous silica nanoparticles (SiNPs) are not only abundant in nature, but also the second largest engineering nanomaterials in terms of annual output. Respiratory exposure is the main route for SiNPs to enter the human body. A large number of studies have focused on the respiratory toxicity of SiNPs and demonstrated that SiNPs could induce pulmonary tissue damage, inflammation, fibrosis, and even the malignant transformation of bronchial epithelial cells, while the size-dependent toxicity of SiNPs and their underlying biological mechanisms remain unclear. In this regard, a transcriptomics study would be conductive to gaining a better understanding of the toxic mechanism. In the present study, microarray analysis was performed to investigate the genome-wide transcriptional alteration induced by different sizes of SiNPs in human primary bronchial epithelial cells (BEAS-2B). To determine the effect of the particle size on the toxicity, nanoparticles of two sizes (41 nm and 61 nm) and submicron particles of one size (206 nm) were introduced. The bioinformatics analysis results indicated that: (1) the number of differentially expressed genes in the three SiNP-treated groups increased with the particle size decreasing; (2) the genes involved in the immune and inflammatory response, gene expression, signal transduction, endoplasmic reticulum stress, oxidative stress, cell metabolism, and cell proliferation were gradually upregulated with the particle size decreasing, while the genes related to the morphological development of the respiratory system were gradually downregulated with the particle size decreasing; (3) the modes of action of the two nanoparticles overlapped with each other to some degree, and there existed many different modes compared to those from the submicron particles; (4) both the silica nanoparticles affected the pathways associated with the cell entry of silica nanoparticles, autophagy and lysosomal dysfunction, endoplasmic reticulum stress, inflammatory response, DNA damage, and gene expression, as well as apoptotic resistance and cancer. To the best of our knowledge, this is the first study that has reported the alteration trend of gene expression profiles with the change in silica particle size. Our study provides a great deal of information on the toxic mechanisms underlying the respiratory toxicity induced by SiNPs, and can also serve as an experimental basis for the toxicity and safety evaluation of silica nanoparticles.

Toxicology of silica nanoparticles: an update

Large-scale production and use of amorphous silica nanoparticles (SiNPs) have increased the risk of human exposure to SiNPs, while their health effects remain unclear. In this review, scientific papers from 2010 to 2016 were systematically selected and sorted based on in vitro and in vivo studies: to provide an update on SiNPs toxicity and to address the knowledge gaps indicated in the review of Napierska (Part Fibre Toxicol 7:39, 2010). Toxicity of SiNPs in vitro is size, dose, and cell type dependent. SiNPs synthesized by wet route exhibited noticeably different biological effects compared to thermal route-based SiNPs. Amorphous SiNPs (particularly colloidal and stöber) induced toxicity via mechanisms similar to crystalline silica. In vivo, route of administration and physico-chemical properties of SiNPs influences the toxicokinetics. Adverse effects were mainly observed in acutely exposed animals, while no significant signs of toxicity were noted in chronically dosed animals. The correlation between in vitro and in vivo toxicity remains less well established mainly due to improper-unrealistic-dosing both in vitro and in vivo. In conclusion, notwithstanding the multiple studies published in recent years, unambiguous linking of physico-chemical properties of SiNPs types to toxicity, bioavailability, or human health effects is not yet possible.

A laboratory study of the performance of the handheld diffusion size classifier (DiSCmini) for various aerosols in the 15-400 nm range

In addition to chemical composition, particle concentration and size are among the main parameters used to characterize exposure to airborne ultrafine or nanoparticles. To assess occupational inhalation exposure, real-time instruments are recommended in recent strategies published. Among portable devices for personal exposure assessment in the workplace, DiSCmini (Matter Aerosol AG, Switzerland) has been identified as a potential candidate with its capacity to measure the airborne nanoparticle concentration and average particle size with good time-resolution. Monodisperse and polydisperse test nanoaerosols of varying compositions and morphologies were produced in the laboratory using the CAIMAN facility. These aerosols covered a range of particle sizes between 15 and 400 nm and number concentrations from 700 to 840,000 cm(-3). The aerosols were used to investigate the behavior of DiSCmini, comparing experimental data to reference data. In spite of a slight tendency to underestimate particle size, all particle diameters, number concentrations and surface area concentrations measured were in the same order of magnitude as reference data. Furthermore, no significant effect due to particle composition or morphology was noted.