The toxicological mode of action and the safety of synthetic amorphous silica-a nanostructured material

Nrf2 protects against oxidative stress induced by SiO2 nanoparticles

Aim: The aim of our study was to explore the role of nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) on the exposure of SiO2 nanoparticles (NPs) and its influence. Materials & methods: To understand the mechanism of NP-induced oxidative stress, the involvement of oxidative-stress-responding transcription factors and the Nrf2/antioxidant reactive element (ARE) signaling pathway in the toxicity of SiO2 NPs’ exposure was investigated via in vivo and in vitro models. Results: A549 cells showed a significant cytotoxic effect while A549-shNrf2 cells showed decreased cell viability after nm-SiO2 exposure. SiO2 NPs’ exposure activated the Nrf2/ARE signaling pathway. Nrf2−/− exposed mice showed increased reactive oxygen species, 8-hydroxyl deoxyguanosine level and decreased total antioxidant capacity. Nrf2/ARE signaling pathway activation disrupted, leading inhibition of heme oxygenase-1 and upregulation of PKR-like endoplasmic-reticulum-regulated kinase. Conclusion: Our findings suggested that Nrf2 could protect against oxidative stress induced by SiO2 NPs, and the Nrf2/ARE pathway might be involved in mild-to-moderate SiO2 NP-induced oxidative stress that was evident from dampened activity of Nrf2.

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.

The combined effects of silicon dioxide nanoparticles and cold air exposure on the metabolism and inflammatory responses in white adipocytes

The potential hazard of nanoparticles (NPs) from air pollution has attracted widespread attention. Though the toxicology of NPs has been intensively studied, few works have been reported on the combined effect of silicon dioxide (SiO2) NPs and cold air exposure at the cellular level. Herein, we evaluated the combined effect of SiO2 NPs and cold exposure on metabolism and the inflammatory responses in white adipocytes by qRT-PCR in vitro. After SiO2 NP or cold exposure, there were significant changes in the expressions of adipogenic genes and proinflammatory cytokine genes in white adipocytes. The mRNA levels of IL-6, IL-8, TNF-α and IL-1β were upregulated by SiO2 NP or cold exposure, and more so in the combined group. The expressions of the proinflammatory cytokine genes IL-6, IL-8, TNF-α and IL-1β increased highly significantly (P < 0.01) in the SiO2 NP alone group and the combined group, compared with the control. The expressions of the cold group tended to be upregulated significantly compared with the control in IL-6 (P < 0.01) and IL-8 (P < 0.05). The results demonstrated that there was antagonistic effect between SiO2 NPs and cold air on the plasticity and metabolism in white adipocytes, where the main effect of cold air on the plasticity and metabolism was significant (P < 0.05). However, there was a synergistic effect between SiO2 NPs and cold air on the toxic effects in white adipocytes, in which the main effect of SiO2 NPs on the toxic effects was significant (P < 0.05). In conclusion, SiO2 NPs combined with cold exposure induced a stronger inflammatory response and influenced the plasticity and metabolism in white adipocytes, accompanied by more serious health hazards.

Silica nanoparticles induced intrinsic apoptosis in neuroblastoma SH-SY5Y cells via CytC/Apaf-1 pathway

The present study was to investigate effects of Silica nanoparticles (SiNPs) on nervous system and explore potential mechanisms in human neuroblastoma cells (SH-SY5Y). Cytotoxicity was detected by cell viability and Lactate dehydrogenase (LDH) release. Flow cytometry analysis was applied to assess mitochondrial membrane potential (MMP) loss, intracellular Ca²⁺ and apoptosis. To clarify the mechanism of SiNPs-induced apoptosis, intrinsic apoptosis-related proteins were detected. Our results showed that SiNPs caused cytotoxicity, cell membrane damage and Ca²⁺ increase in a dose-dependent manner in SH-SY5Y cells. Both the mitochondrial membrane potential (MMP) loss and potential mitochondria damage resulted in Cyt C release to the cytoplasm. The elevated Cyt C and Apaf1 further triggered intrinsic apoptosis via executive molecular caspase-9 and caspase-3. The present study confirmed that SiNPs induced intrinsic apoptosis in neuroblastoma SH-SY5Y cells via CytC/Apaf-1 pathway and provided a better understanding of the potential toxicity induced by SiNPs on human neurocyte.

Silica nanoparticles and lead acetate co-exposure triggered synergistic cytotoxicity in A549 cells through potentiation of mitochondria-dependent apoptosis induction

The adverse effects of PM2.5 are the results of combined toxicities of finer particles and their adsorbed toxic pollutants. Nevertheless, the combined toxicity of finer particles and air pollutants still remains unclear. The present study was therefore undertaken to investigate the combined cytotoxicity of silica nanoparticles (nano-SiO₂, a typical atmospheric ultrafine particle) and lead acetate (Pb, a representative air pollutant) in A549 cells focusing on mitochondria-dependent apoptosis induction. The results showed that Pb exposure alone induced mitochondria-dependent apoptosis in A549 cells, as evidenced by increased apoptotic rate and Bax/Bcl-2 ratio, up-regulated caspases 3 and 9 expressions as well as decreased mitochondrial membrane potential. Non-cytotoxic concentration of nano-SiO₂ exposure alone did not trigger apoptosis in A549 cells, but potentialized the apoptotic changes when co-exposure with Pb. Factorial analyses revealed synergistic interactions were responsible for the potentiation of joint apoptotic responses.

Silica nanoparticles as sources of silicic acid favoring wound healing in vitro

There is good evidence that certain silicon-containing materials promote would healing and their common feature is the delivery of orthosilicic acid (Si(OH)₄) either directly or following metabolism. In this respect, amorphous silica nanoparticles (NP), which dissolve in aqueous environments releasing up to 2mM orthosilicic acid, may be appropriate 'slow release' vehicles for bioactive silicon. Here we studied the impact of silica NP suspensions (primary particles∼10nm) in undersaturated conditions (below 2mM Si) with differing degrees of surface charge and dissolution rate on human dermal fibroblasts (CCD-25SK cells) viability, proliferation and migration in a cellular wound model. Silica was shown to be non-toxic for all forms and concentrations tested and whilst the anticipated stimulatory effect of orthosilicic acid was observed, the silica NPs also stimulated fibroblast proliferation and migration. In particular, the amine-functionalized particles promoted wound closure more rapidly than soluble orthosilicic acid alone. We suggest that this effect is related to easy cellular internalization of these particles followed by their intracellular dissolution releasing silicic acid at a faster rate than its direct uptake from the medium. Our findings indicate that amorphous silica-based NPs may favour the delivery and release of bioactive silicic acid to cells, promoting wound healing.

Combined Effect of Silica Nanoparticles and Benzo[a]pyrene on Cell Cycle Arrest Induction and Apoptosis in Human Umbilical Vein Endothelial Cells

Particulate matter (PM) such as ultrafine particulate matter (UFP) and the organic compound pollutants such as polycyclic aromatic hydrocarbon (PAH) are widespread in the environment. UFP and PAH are present in the air, and their presence may enhance their individual adverse effects on human health. However, the mechanism and effect of their combined interactions on human cells are not well understood. We investigated the combined toxicity of silica nanoparticles (SiNPs) (UFP) and Benzo[a]pyrene (B[a]P) (PAH) on human endothelial cells. Human umbilical vascular endothelial cells (HUVECs) were exposed to SiNPs or B[a]P, or a combination of SiNPs and B[a]P. The toxicity was investigated by assessing cellular oxidative stress, DNA damage, cell cycle arrest, and apoptosis. Our results show that SiNPs were able to induce reactive oxygen species generation (ROS). B[a]P, when acting alone, had no toxicity effect. However, a co-exposure of SiNPs and B[a]P synergistically induced DNA damage, oxidative stress, cell cycle arrest at the G2/M check point, and apoptosis. The co-exposure induced G2/M arrest through the upregulation of Chk1 and downregulation of Cdc25C, cyclin B1. The co-exposure also upregulated bax, caspase-3, and caspase-9, the proapoptic proteins, while down-regulating bcl-2, which is an antiapoptotic protein. These results show that interactions between SiNPs and B[a]P synergistically potentiated toxicological effects on HUVECs. This information should help further our understanding of the combined toxicity of PAH and UFP.

Ecophysiological perspectives on engineered nanomaterial toxicity in fish and crustaceans

Engineered nanomaterials (ENMs) are incorporated into numerous industrial, clinical, food, and consumer products and a significant body of evidence is now available on their toxicity to aquatic organisms. Environmental ENM concentrations are difficult to quantify, but production and release estimates suggest wastewater treatment plant effluent levels ranging from 10^-4 to >10¹μgL^-1 for the most common formulations by production volume. Bioavailability and ENM toxicity are heavily influenced by water quality parameters and the physicochemical properties and resulting colloidal behaviour of the particular ENM formulation. ENMs generally induce only mild acute toxicity to most adult fish and crustaceans under environmentally relevant exposure scenarios; however, sensitivity may be considerably higher for certain species and life stages. In adult animals, aquatic ENM exposure often irritates respiratory and digestive epithelia and causes oxidative stress, which can be associated with cardiovascular dysfunction and the activation of immune responses. Direct interactions between ENMs (or their dissolution products) and proteins can also lead to ionoregulatory stress and/or developmental toxicity. Chronic and developmental toxicity have been noted for several common ENMs (e.g. TiO₂, Ag), however more data is necessary to accurately characterize long term ecological risks. The bioavailability of ENMs should be limited in saline waters but toxicity has been observed in marine animals, highlighting a need for more study on possible impacts in estuarine and coastal systems. Nano-enabled advancements in industrial processes like water treatment and remediation could provide significant net benefits to the environment and will likely temper the relatively modest impacts of incidental ENM release and exposure.

Differential cytotoxic and inflammatory potency of amorphous silicon dioxide nanoparticles of similar size in multiple cell lines

The likelihood of environmental and health impacts of silicon dioxide nanoparticles (SiNPs) has risen, due to their increased use in products and applications. The biological potency of a set of similarly-sized amorphous SiNPs was investigated in a variety of cells to examine the influence of physico-chemical and biological factors on their toxicity. Cellular LDH and ATP, BrdU incorporation, resazurin reduction and cytokine release were measured in human epithelial A549, human THP-1 and mouse J774A.1 macrophage cells exposed for 24 h to suspensions of 5-15, 10-20 and 12 nm SiNPs and reference particles. The SiNPs were characterized in dry state and in suspension to determine their physico-chemical properties. The dose-response data were simplified into particle potency estimates to facilitate the comparison of multiple endpoints of biological effects in cells. Mouse macrophages were the most sensitive to SiNP exposures. Cytotoxicity of the individual cell lines was correlated while the cytokine responses differed, supported by cell type-specific differences in inflammation-associated pathways. SiNP (12 nm), the most cytotoxic and inflammogenic nanoparticle had the highest surface acidity, dry-state agglomerate size, the lowest trace metal and organics content, the smallest surface area and agglomerate size in suspension. Particle surface acidity appeared to be the most significant determinant of the overall biological activity of this set of nanoparticles. Combined with the nanoparticle characterization, integration of the biological potency estimates enabled a comprehensive determination of the cellular reactivity of the SiNPs. The approach shows promise as a useful tool for first-tier screening of SiNP toxicity.

Cross-Sectional Study on Nonmalignant Respiratory Morbidity due to Exposure to Synthetic Amorphous Silica

OBJECTIVES

The aim of this study was to assess the health impact of chronic exposure to synthetic amorphous silica (SAS) on nonmalignant respiratory morbidity.

METHODS

We used multiple linear and logistic regression models and Monte Carlo multimodel analyses of two exposure scenarios to evaluate the effect of cumulative exposure to inhalable SAS dust on symptoms, spirometry, and chest films in 462 male workers from five German SAS-producing plants.

RESULTS

Exposure to SAS was associated with a reduction in forced vital capacity (FVC) in one of the two exposure scenarios but had no effect on forced expiratory volume in 1 second (FEV1) or FEV1/FVC in either exposure scenario. Monte Carlo analysis indicated a decline in FVC of -11 mL per 10 mg/m-years exposure (-6 to -0.4). Chest films showed no evidence of pneumoconiosis.

CONCLUSION

This study provides limited evidence of minor dose-related effects of chronic exposure to SAS on lung function.

Amorphous Silica Particles Relevant in Food Industry Influence Cellular Growth and Associated Signaling Pathways in Human Gastric Carcinoma Cells

Nanostructured silica particles are commonly used in biomedical and biotechnical fields, as well as, in cosmetics and food industry. Thus, their environmental and health impacts are of great interest and effects after oral uptake are only rarely investigated. In the present study, the toxicological effects of commercially available nano-scaled silica with a nominal primary diameter of 12 nm were investigated on the human gastric carcinoma cell line GXF251L. Besides the analysis of cytotoxic and proliferative effects and the comparison with effects of particles with a nominal primary diameter of 200 nm, emphasis was also given to their influence on the cellular epidermal growth factor receptor (EGFR) and mitogen-activated protein kinases (MAPK) signaling pathways—both of them deeply involved in the regulation of cellular processes like cell cycle progression, differentiation or proliferation. The investigated silica nanoparticles (NPs) were found to stimulate cell proliferation as measured by microscopy and the sulforhodamine B assay. In accordance, the nuclear level of the proliferation marker Ki-67 was enhanced in a concentration-dependent manner. At high particle concentrations also necrosis was induced. Finally, silica NPs affected the EGFR and MAPK pathways at various levels dependent on concentration and time. However, classical activation of the EGFR, to be reflected by enhanced levels of phosphorylation, could be excluded as major trigger of the proliferative stimulus. After 45 min of incubation the level of phosphorylated EGFR did not increase, whereas enhanced levels of total EGFR protein were observed. These results indicate interference with the complex homeostasis of the EGFR protein, whereby up to 24 h no impact on the transcription level was detected. In addition, downstream on the level of the MAP kinases ERK1/2 short term incubation appeared to affect total protein levels without clear increase in phosphorylation. Depending on the concentration range, enhanced levels of ERK1/2 phosphorylation were only observed after 24 h of incubation. Taken together, the present study demonstrates the potential of the tested silica particles to enhance the growth of gastric carcinoma cells. Although interference with the EGFR/MAPK cascade is observed, additional mechanisms are likely to be involved in the onset of the proliferative stimulus.

From Dose to Response: In Vivo Nanoparticle Processing and Potential Toxicity

Adverse human health impacts due to occupational and environmental exposures to manufactured nanoparticles are of concern and pose a potential threat to the continued industrial use and integration of nanomaterials into commercial products. This chapter addresses the inter-relationship between dose and response and will elucidate on how the dynamic chemical and physical transformation and breakdown of the nanoparticles at the cellular and subcellular levels can lead to the in vivo formation of new reaction products. The dose-response relationship is complicated by the continuous physicochemical transformations in the nanoparticles induced by the dynamics of the biological system, where dose, bio-processing, and response are related in a non-linear manner. Nanoscale alterations are monitored using high-resolution imaging combined with in situ elemental analysis and emphasis is placed on the importance of the precision of characterization. The result is an in-depth understanding of the starting particles, the particle transformation in a biological environment, and the physiological response.

Silica dioxide nanoparticles combined with cold exposure induce stronger systemic inflammatory response

Growing concern has been raised over the potential hazard of nanoparticles (NPs) on human health from ambient particulate air pollution. Silicon dioxide (SiO₂) NPs are one of the most widely used nanoparticles in many sectors of industry. Research on NPs has focused mainly on their toxicity in organs. Meanwhile, NPs are present in the air year-round, but are more serious in winter. Thus, the aim of this study was to evaluate the inflammatory response to SiO₂ NPs using in vivo test systems. The composition of particulate matter is complicated; however, elemental silicon accounts for a significant proportion. Cold exposure can induce many kinds of systemic reactions. Thus, the second aim of this study was also to evaluate the combined effect of NPs and cold exposure on human health. There is little research on the combined effects of nanoparticles and cold on inflammation. Sprague-Dawley rats were randomly divided into four groups: those exposed to SiO₂ NPs by intratracheal instillation, those exposed to at 4 °C 4 h/day for 4 weeks, a combined SiO₂ NPs and cold exposure group, and a control group. Inflammatory cell infiltration in the lungs was mainly observed after exposure to SiO₂ NPs or cold. Hematoxylin and eosin staining revealed that inflammation of the lungs was more serious in the combined group. In the white adipose tissue and brown adipose tissue of the combined groups, the mRNA expressions of pro-inflammatory cytokines were upregulated. In conclusion, SiO₂ NPs combined with cold exposure induced a stronger systemic inflammatory response, accompanied by more serious health hazards.

Comparing the CORAL and Random Forest Approaches for Modelling the In Vitro Cytotoxicity of Silica Nanomaterials

Nanotechnology is one of the most important technological developments of the 21st century. In silico methods to predict toxicity, such as quantitative structure–activity relationships (QSARs), promote the safe-by-design approach for the development of new materials, including nanomaterials. In this study, a set of cytotoxicity experimental data corresponding to 19 data points for silica nanomaterials were investigated, to compare the widely employed CORAL and Random Forest approaches in terms of their usefulness for developing so-called ‘nano-QSAR’ models. ‘External’ leave-one-out cross-validation (LOO) analysis was performed, to validate the two different approaches. An analysis of variable importance measures and signed feature contributions for both algorithms was undertaken, in order to interpret the models developed. CORAL showed a more pronounced difference between the average coefficient of determination (R2) for training and for LOO (0.83 and 0.65 for training and LOO, respectively), compared to Random Forest (0.87 and 0.78 without bootstrap sampling, 0.90 and 0.78 with bootstrap sampling), which may be due to overfitting. With regard to the physicochemical properties of the nanomaterials, the aspect ratio and zeta potential were found to be the two most important variables for Random Forest, and the average feature contributions calculated for the corresponding descriptors were consistent with the clear trends observed in the data set: less negative zeta potential values and lower aspect ratio values were associated with higher cytotoxicity. In contrast, CORAL failed to capture these trends.

The safety of nanostructured synthetic amorphous silica (SAS) as a food additive (E 551)

KEY MESSAGES

Particle sizes of E 551 products are in the micrometre range. The typical external diameters of the constituent particles (aggregates) are greater than 100 nm. E 551 does not break down under acidic conditions such as in the stomach, but may release dissolved silica in environments with higher pH such as the intestinal tract. E 551 is one of the toxicologically most intensively studied substances and has not shown any relevant systemic or local toxicity after oral exposure. Synthetic amorphous silica (SAS) meeting the specifications for use as a food additive (E 551) is and has always been produced by the same two production methods: the thermal and the wet processes, resulting in E 551 products consisting of particles typically in the micrometre size range. The constituent particles (aggregates) are typically larger than 100 nm and do not contain discernible primary particles. Particle sizes above 100 nm are necessary for E 551 to fulfil its technical function as spacer between food particles, thus avoiding the caking of food particles. Based on an in-depth review of the available toxicological information and intake data, it is concluded that the SAS products specified for use as food additive E 551 do not cause adverse effects in oral repeated-dose studies including doses that exceed current OECD guideline recommendations. In particular, there is no evidence for liver toxicity after oral intake. No adverse effects have been found in oral fertility and developmental toxicity studies, nor are there any indications from in vivo studies for an immunotoxic or neurotoxic effect. SAS is neither mutagenic nor genotoxic in vivo. In intact cells, a direct interaction of unlabelled and unmodified SAS with DNA was never found. Differences in the magnitude of biological responses between pyrogenic and precipitated silica described in some in vitro studies with murine macrophages at exaggerated exposure levels seem to be related to interactions with cell culture proteins and cell membranes. The in vivo studies do not indicate that there is a toxicologically relevant difference between SAS products after oral exposure. It is noted that any silicon dioxide product not meeting established specifications, and/or produced to provide new functionality in food, requires its own specific safety and risk assessment.

Genotoxic effects of synthetic amorphous silica nanoparticles in the mouse lymphoma assay

Synthetic amorphous silica nanoparticles (SAS NPs) have been used in various industries, such as plastics, glass, paints, electronics, synthetic rubber, in pharmaceutical drug tablets, and a as food additive in many processed foods. There are few studies in the literature on NPs using gene mutation approaches in mammalian cells, which represents an important gap for genotoxic risk estimations. To fill this gap, the mouse lymphoma L5178Y/Tk^+/− assay (MLA) was used to evaluate the mutagenic effect for five different concentrations (from 0.01 to 150 μg/mL) of two different sizes of SAS NPs (7.172 and 7.652 nm) and a fine collodial form of silicon dioxide (SiO₂). This assay detects a broad spectrum of mutational events, from point mutations to chromosome alterations. The results obtained indicate that the two selected SAS NPs are mutagenic in the MLA assay, showing a concentration-dependent effect. The relative mutagenic potencies according to the induced mutant frequency (IMF) are as follows: SAS NPs (7.172 nm) (IMF = 705.5 × 10⁻⁶), SAS NPs (7.652 nm) (IMF = 575.5 × 10⁻⁶), and SiO₂ (IMF = 57.5 × 10⁻⁶). These in vitro results, obtained from mouse lymphoma cells, support the genotoxic potential of NPs as well as focus the discussion of the benefits/risks associated with their use in different areas.

Active diffusion of nanoparticles of maternal origin within the embryonic brain

Aim: To investigate porous silicon (PSi) nanoparticles (NPs) behavior in the embryonic brain. Materials & methods: Fluorescently labeled PSi NPs were injected into the embryonic brains intraventricularly and to the mother intravenously (iv.). Brain histology from different time points up to 3 days was analyzed and live brains imaged with two-photon microscopy. Results: PSi NPs were able to penetrate 80% of the embryonic cortical depth. Particle motility was confirmed in real-time in vivo. PSi NPs were able to penetrate the embryonic cortex after either iv. maternal or intraventricular injection. No developmental of macromorphological changes or increased cell apoptosis was observed. Conclusion: PSi NPs penetrate deep in the brain tissues of embryos after intraventricular injection and after iv. injection to the mother.

In Vitro Cytotoxicity of Maxillofacial Silicone Elastomers: Effect of Nano-particles

PURPOSE

Silicone elastomers are generally used for maxillofacial extraoral prostheses. The purpose of this in vitro study was to evaluate the cytotoxicity of different kinds of nanoparticles added to two types of maxillofacial elastomers.

MATERIALS AND METHODS

A-2000 and A-2006 silicone elastomers were used. The silicone specimens were divided into eight groups according to the presence of additional nanoparticles (n = 18). The following represents the groups in the study: Group A: A-2000 silicone (control group); Group B: A-2006 silicone (control group); Group C: A-2000 silicone and the addition of titanium dioxide (TiO₂ ); Group D: A-2006 silicone and the addition of TiO₂ ; Group E: A-2000 silicone and the addition of fumed silica; Group F: A-2006 silicone and the addition of fumed silica; Group G: A-2000 silicone and the addition of silaned silica; Group H: A-2006 silicone and the addition of silaned silica. A paired sample t-test was used to analyze the cytotoxicity of each group after 24, 48, and 72 hours.

RESULTS

Based on the results of the 24-hour analysis, the biocompatibility values of the (A-2006) fumed silica group were higher than those of the control groups. There was no statistically significant difference in A-2006 and A-2000 groups. The cytotoxicity values of the control groups and TiO₂ (A-2000 silicone) elastomer groups increased at all test times; however, the cytotoxicity values of the TiO₂ (A-2006), fumed silica (A-2006), silaned silica (A-2006), fumed silica (A-2000), and silaned silica (A-2000) groups increased significantly only from 24 to 48 hours.

CONCLUSION

Nanoparticles of TiO₂ , fumed silica, and silaned silica added to a commercial silicone-based elastomer used for fabrication of maxillofacial prostheses are nontoxic.

Silica nanoparticles induce start inhibition of meiosis and cell cycle arrest via down-regulating meiotic relevant factors

Silica nanoparticles have been shown to induce reproductive toxicity, but the mechanism is unknown. To investigate the toxic mechanism of SiNPs, 60 male mice were randomly divided into three groups: a control group, a saline group and a SiNPs group, with two evaluation time points (45 and 75 days after the first dose) per group. Mice in the SiNPs group were treated with SiNPs at a dose of 2.0 mg kg-1 every three days, a total of 15 times in 45 days, mice in the saline group were given the same volume of physiological saline, and the control group was treated with nothing. Then, half of the mice in each group were sacrificed for tissue samples on days 45 and 75. In vitro, GC-2spd cells were exposed to various concentrations of SiNPs for 24 h. The results showed that SiNPs damaged seminiferous epithelium, leading to a decrease in sperm quality and an increase in the sperm abnormality rate. Moreover, expressions of Sohlh1/cyclin A1/cyclin B1/CDK1/CDK2 were greatly down-regulated and the ROS level in the testicular tissue of the mice was significantly increased on day 45. However, these changes were reversed by day 75. In vitro, SiNPs induced G0/G1-phase cell cycle arrest and proliferation inhibition in GC-2spd cells. These results suggested that SiNPs might induce cell cycle arrest and inhibit cell proliferation by down-regulating expressions of meiotic regulators, whereas DNA damage caused by oxidative stress may be associated with meiosis and sperm production. In addition, damage to the male reproductive system caused by SiNPs may be reversible.

Repetitive Dosing of Fumed Silica Leads to Profibrogenic Effects through Unique Structure-Activity Relationships and Biopersistence in the Lung

Contrary to the notion that the use of fumed silica in consumer products can "generally (be) regarded as safe" (GRAS), the high surface reactivity of pyrogenic silica differs from other forms of synthetic amorphous silica (SAS), including the capacity to induce membrane damage and acute proinflammatory changes in the murine lung. In addition, the chain-like structure and reactive surface silanols also allow fumed silica to activate the NLRP3 inflammasome, leading to IL-1β production. This pathway is known to be associated with subchronic inflammation and profibrogenic effects in the lung by α-quartz and carbon nanotubes. However, different from the latter materials, bolus dose instillation of 21 mg/kg fumed silica did not induce sustained IL-1β production or subchronic pulmonary effects. In contrast, the NLRP3 inflammasome pathway was continuously activated by repetitive-dose administration of 3 × 7 mg/kg fumed silica, 1 week apart. We also found that while single-dose exposure failed to induce profibrotic effects in the lung, repetitive dosing can trigger increased collagen production, even at 3 × 3 mg/kg. The change between bolus and repetitive dosing was due to a change in lung clearance, with recurrent dosing leading to fumed silica biopersistence, sustained macrophage recruitment, and activation of the NLRP3 pathway. These subchronic proinflammatory effects disappeared when less surface-reactive titanium-doped fumed silica was used for recurrent administration. All considered, these data indicate that while fumed silica may be regarded as safe for some applications, we should reconsider the GRAS label during repetitive or chronic inhalation exposure conditions.

Inhaled SiO2 nanoparticles blunt cold-exposure-induced WAT-browning and metabolism activation in white and brown adipose tissue

Concern has been growing over the potential hazard of nanoparticles to human health because of increasing ambient particulate air pollution. Much research has been performed on the toxicology of nanoparticles to organs. Meanwhile, particles floating in air, particularly in winter, are more serious. Thus, the purpose of this study was to evaluate the effect of nanoparticles and cold on human health. There is little research on the effects of nanoparticles on energy metabolism. The composition of particulate matter is complicated; however, silicon in particles accounts for a significant proportion. Adipose tissue is the main organ that produces heat and maintains the body temperature in a cold environment. White adipose tissue (WAT) stores energy in the form of triacylglycerol, whereas brown adipose tissue (BAT) dissipates energy in the form of heat to maintain the body temperature. This article presents the effect of air ultra-particles and cold on the WAT and BAT. In vivo, Sprague-Dawley rats were divided into four groups: exposed to the same deposited doses of silicon dioxide (SiO₂) nanoparticles (NPs) by intratracheal instillation or/and cold exposure at 4 °C, 4 h per day for four weeks. Cold exposure induced weight loss and WAT browning, as indicated by pathology, transmission electron microscopy (TEM), upregulated mRNA levels of BAT and WAT specific genes and molecular switches. Intratracheal instillation of nano-SiO₂ induced a slowdown in metabolism, weight gain and inhibited WAT browning, as indicated by the downregulated mRNA levels of BAT and WAT marker genes and molecular switches. This study provided direct evidence that SiO₂ NPs might inhibit the effect of cold-induced white/brown adipose tissue changes in plasticity and metabolism.

Functionalized Mesoporous Silica Nanoparticle with Antioxidants as a New Carrier That Generates Lower Oxidative Stress Impact on Cells

Mesoporous silica nanoparticles (MSNs) were covalently coated with antioxidant molecules, namely, caffeic acid (MSN-CAF) or rutin (MSN-RUT), in order to diminish the impact of oxidative stress induced after transfection into cells, thus generating safer carriers used for either drug delivery or other applications. Two cellular models involved in the entry of NPs in the body were used for this purpose: the intestinal Caco-2 and the epidermal HaCaT cell lines. Rutin gave the best results in terms of antioxidant capacities preservation during coupling procedures, cellular toxicity alleviation, and decrease of ROS level after 24 h incubation of cells with grafted nanoparticles. These protective effects of rutin were found more pronounced in HaCaT than in Caco-2 cells, indicating some cellular specificity toward defense against oxidative stress. In order to gain more insight about the Nrf2 response, a stable transfected HaCaT cell line bearing repeats of the antioxidant response element (ARE) in front of a luciferase reporter gene was generated. In this cell line, both tBHQ and quercetin (Nrf2 agonists), but not rutin, were able to induce, in a dose-dependent fashion, the luciferase response. Interestingly, at high concentration, MSN-RUT was able to induce a strong Nrf2 protective response in HaCaT cells, accompanied by a comparable induction of HO-1 mRNA. The level of these responses was again less important in Caco-2 cells. To conclude, in keratinocyte cell line, the coupling of rutin to silica nanoparticles was beneficial in term of ROS reduction, cellular viability, and protective effects mediated through the activation of the Nrf2 antioxidant pathway.

Critical review of the safety assessment of nano-structured silica additives in food

The development of nano-materials is viewed as one of the most important technological advances of the 21st century and new applications of nano-sized particles in the production, processing, packaging or storage of food are expected to emerge soon. This trend of growing commercialization of engineered nano-particles as part of modern diet will substantially increase oral exposure. Contrary to the proven benefits of nano-materials, however, possible adverse health effects have generally received less attention. This problem is very well illustrated by nano-structured synthetic amorphous silica (SAS), which is a common food additive since several decades although the relevant risk assessment has never been satisfactorily completed. A no observed adverse effect level of 2500 mg SAS particles/kg body weight per day was derived from the only available long-term administration study in rodents. However, extrapolation to a safe daily intake for humans is problematic due to limitations of this chronic animal study and knowledge gaps as to possible local intestinal effects of SAS particles, primarily on the gut-associated lymphoid system. This uncertainty is aggravated by digestion experiments indicating that dietary SAS particles preserve their nano-sized structure when reaching the intestinal lumen. An important aspect is whether food-borne particles like SAS alter the function of dendritic cells that, embedded in the intestinal mucosa, act as first-line sentinels of foreign materials. We conclude that nano-particles do not represent a completely new threat and that most potential risks can be assessed following procedures established for conventional chemical hazards. However, specific properties of food-borne nano-particles should be further examined and, for that purpose, in vitro tests with decision-making cells of the immune system are needed to complement existing in vivo studies.

Silica nanoparticles induce reversible damage of spermatogenic cells via RIPK1 signal pathways in C57 mice

The reproductive toxicity of silica nanoparticles (SiNPs) is well known, but the underlying mechanism is still not clear. To investigate the toxic mechanism of SiNPs on spermatogenic cells, 60 C57 male mice were randomly and equally divided into three groups (the control group, the saline control group, and the SiNPs group) with two observed time points (45 days and 75 days). The mice in the SiNPs group were administered with SiNPs 2 mg/kg diluted in normal saline, and the mice of the saline control group were given equivoluminal normal saline by tracheal perfusion every 3 days for 45 days (in total 15 times). The control group mice were bred without treatment. In each group, a half number of the mice were sacrificed on the 45th day after the first dose, and the remaining half were sacrificed on the 75th day. The results showed that SiNPs increased the malformation of sperms and decreased the motility and concentration of sperms in epididymis on the 45th day after the first dose. SiNPs induced oxidative stress in testis and led to apoptosis and necroptosis of the spermatogenic cells. Furthermore, SiNPs increased the expression of Fas/FasL/RIPK1/FADD/caspase-8/caspase-3 and RIPK3/MLKL on the 45th day after the first dose. However, compared with the saline control group, the index of sperms and the expression of Fas/FasL/RIPK1/FADD/caspase-8/caspase-3/RIPK3/MLKL showed no significant changes in the SiNPs group on the 75th day after the first dose. These data suggested that SiNPs could induce apoptosis and necroptosis in the spermatogenic cells by activating the RIPK1 pathway resulting from oxidative stress in male mice. SiNPs-induced damage recovered on the 75th day after the first dose, which suggested that SiNPs-induced toxicity is reversible.

Relaxivity and toxicological properties of manganese oxide nanoparticles for MRI applications

Manganese oxide nanoparticles (MONs) have received growing attention as alternative T ₁ MRI contrast agents due to the association of commercial gadolinium-based contrast agents with nephrogenic systemic fibrosis. Since the seminal publication first describing the use of MONs as positive T ₁ contrast agents, there is an ongoing impetus to develop MONs of higher T ₁ signal intensity for better diagnostic efficacy. Indeed, various MON-based nanoprobe designs have been proposed, such as the employment of a mesoporous nanomaterial with MONs evenly dispersed within, or the traditional coating of a biocompatible layer onto the surface of MONs to form a core-shell configuration. Recent advances in this field also propose stimuli-responsive MONs that capitalize on an acidic dissolution or in situ reduction to release Mn²⁺ ions for a multi-fold increase in MRI contrast. However, the potential nanotoxicity of MONs remains a key obstacle to the clinical translation of MON-based T ₁ contrast agents. Due to the wide variety of functionalities and physicochemical properties of MONs, there is also a lack of consensus on the toxicological properties of MONs. In addition, the r ₁ relaxivity of MRI contrast agents typically decreases at higher field strength. Hence, it highlights the need to develop MON-based contrast agents with higher relaxivities. In this regard, this article aims to present a thorough review of MONs for MRI applications, with particular emphasis on their relaxivity and toxicological properties. In order to systematically review the current state-of-the-art for the development of MONs for MRI applications, the MON-based T ₁ contrast agents are categorized based on the structure of the nanomaterial system. Key parameters that influence the nanotoxicity of MONs are also examined while the absorption, distribution, metabolism and excretion of MON in vivo are evaluated to discern how long the nanoparticles will be present within the body, as well as to predict the organs or tissues in which they distribute.

Autophagy and autophagy dysfunction contribute to apoptosis in HepG2 cells exposed to nanosilica

Great concerns have led to the evaluation of the potential hazards of nanosilica to human health and the environment. However, there still exists persistent debates on the biological effects and toxic consequences induced by nanosilica. The present study investigated both autophagy and apoptosis in ICR mice and Human hepatocellular carcinoma cells (HepG2), and then explored the interactive mechanism between these two distinct cell death modalities in HepG2 cells. Mice liver injuries seen by hematoxylin and eosin (HE) staining indicated the hepatotoxic effects of nanosilica. The TUNEL assay and immunohistochemistry results confirmed that nanosilica could induce both apoptosis and autophagy in vivo. Flow cytometry analysis demonstrated apoptosis induction in vitro, while autophagic ultrastructures, LC3-II expression and immunofluorescence clarified autophagy activation by nanosilica. Apoptosis suppression by the autophagy inhibitor of 3-methyladenine (3-MA) implied that autophagy was involved in apoptotic cell death. A mechanistic study verified that nanosilica induced autophagy via negative regulation of mammalian target of rapamycin (mTOR) signaling but not the Beclin-1 associated pathway. The enhancement of p62 accumulation and mTOR down-regulation might account for the molecular mechanism in contribution of autophagy to apoptosis. As an emerging new mechanism of nanomaterial toxicity, autophagy might be a more susceptive indicator for toxicological consequence evaluation in nanoparticle toxicity. The present study provides novel evidence to elucidate the toxicity mechanisms and may be beneficial to more rational applications of nanosilica in the future.

Interactions between Silicon Oxide Nanoparticles (SONPs) and U(VI) Contaminations: Effects of pH, Temperature and Natural Organic Matters

The interactions between contaminations of U(VI) and silicon oxide nanoparticles (SONPs), both of which have been widely used in modern industry and induced serious environmental challenge due to their high mobility, bioavailability, and toxicity, were studied under different environmental conditions such as pH, temperature, and natural organic matters (NOMs) by using both batch and spectroscopic approaches. The results showed that the accumulation process, i.e., sorption, of U(VI) on SONPs was strongly dependent on pH and ionic strength, demonstrating that possible outer- and/or inner-sphere complexes were controlling the sorption process of U(VI) on SONPs in the observed pH range. Humic acid (HA), one dominated component of NOMs, bounded SONPs can enhance U(VI) sorption below pH~4.5, whereas restrain at high pH range. The reversible sorption of U(VI) on SONPs possibly indicated that the outer-sphere complexes were prevalent at pH 5. However, an irreversible interaction of U(VI) was observed in the presence of HA (Fig 1). It was mainly due to the ternary SONPs-HA-U(VI) complexes (Type A Complexes). After SONPs adsorbed U(VI), the particle size in suspension was apparently increased from ~240 nm to ~350 nm. These results showed that toxicity of both SONPs and U(VI) will decrease to some extent after the interaction in the environment. These findings are key for providing useful information on the possible mutual interactions among different contaminants in the environment.

Drosophila melanogaster as a suitable in vivo model to determine potential side effects of nanomaterials: A review

Despite being a relatively new field, nanoscience has been in the forefront among many scientific areas. Nanoparticle materials (NM) present interesting physicochemical characteristics not necessarily found in their bulky forms, and alterations in their size or coating markedly modify their physical, chemical, and biological properties. Due to these novel properties there is a general trend to exploit these NM in several fields of science, particularly in medicine and industry. The increased presence of NM in the environment warrants evaluation of potential harmful effects in order to protect both environment and human exposed populations. Although in vitro approaches are commonly used to determine potential adverse effects of NM, in vivo studies generate data expected to be more relevant for risk assessment. As an in vivo model Drosophila melanogaster was previously found to possess reliable utility in determining the biological effects of NM, and thus its usage increased markedly over the last few years. The aims of this review are to present a comprehensive overview of all apparent studies carried out with NM and Drosophila, to attain a clear and comprehensive picture of the potential risk of NM exposure to health, and to demonstrate the advantages of using Drosophila in nanotoxicological investigations.

Amorphous silica nanoparticle-induced perturbation of cholesterol homeostasis as a function of surface area highlights safe-by-design implementation: an integrated multi-OMICS analysis

The systems toxicology approach revealed that the alterations of cholesterol biosynthesis were directly proportional with the surface area of amorphous silica nanoparticles (aSiNPs); the larger the surface area the higher the cholesterol level.

Combined exposure to nano-silica and lead induced potentiation of oxidative stress and DNA damage in human lung epithelial cells

Growing evidence has confirmed that exposure to ambient particulate matters (PM) is associated with increased morbidity and mortality of cardiovascular and pulmonary diseases. Ambient PM is a complex mixture of particles and air pollutants. Harmful effects of PM are specifically associated with ultrafine particles (UFPs) that can adsorb high concentrations of toxic air pollutants and are easily inhaled into the lungs. However, combined effects of UFPs and air pollutants on human health remain unclear. In the present study, we elucidated the combined toxicity of silica nanoparticles (nano-SiO2), a typical UFP, and lead acetate (Pb), a typical air pollutant. Lung adenocarcinoma A549 cells were exposed to nano-SiO2 and Pb alone or their combination, and their combined toxicity was investigated by focusing on cellular oxidative stress and DNA damage. Factorial analyses were performed to determine the potential interactions between nano-SiO2 and Pb. Our results showed that exposure of A549 cells to a modest cytotoxic concentration of Pb alone induced oxidative stress, as evidenced by elevated reactive oxygen species generation and lipid peroxidation, and reduced glutathione content and superoxide dismutase and glutathione peroxidase activities. In addition, exposure of A549 cells to Pb alone induced DNA damage, as evaluated by alkaline comet assay. Exposure of A549 cells to non-cytotoxic concentration of nano-SiO2 did not induce cellular oxidative stress and DNA damage. However, exposure to the combination of nano-SiO2 and Pb potentiated oxidative stress and DNA damage in A549 cells. Factorial analyses indicated that the potentiation of combined toxicity of nano-SiO2 and Pb was induced by additive or synergistic interactions.

Nanotoxicology and Metalloestrogens: Possible Involvement in Breast Cancer

As the use of nanotechnology has expanded, an increased number of metallic oxides have been manufactured, yet toxicology testing has lagged significantly. Metals used in nano-products include titanium, silicon, aluminum, silver, zinc, cadmium, cobalt, antimony, gold, etc. Even the noble metals, platinum and cerium, have been used as a treatment for cancer, but the toxicity of these metals is still unknown. Significant advances have been made in our understanding and treatment of breast cancer, yet millions of women will experience invasive breast cancer in their lifetime. The pathogenesis of breast cancer can involve multiple factors; (1) genetic; (2) environmental; and (3) lifestyle-related factors. This review focuses on exposure to highly toxic metals, ("metalloestrogens" or "endocrine disruptors") that are used as the metallic foundation for nanoparticle production and are found in a variety of consumer products such as cosmetics, household items, and processed foods, etc. The linkage between well-understood metalloestrogens such as cadmium, the use of these metals in the production of nanoparticles, and the relationship between their potential estrogenic effects and the development of breast cancer will be explored. This will underscore the need for additional testing of materials used in nano-products. Clearly, a significant amount of work needs to be done to further our understanding of these metals and their potential role in the pathogenesis of breast cancer.

Balanced TH1 and TH2 immunopotentiating effects of silicates partly containing nanoparticles present in calcined serpentine

Calcined Serpentine (CS) is used in various formulations of alternative systems of medicine as a tonic to vital organs and as an anti-inflammatory agent. The process of calcination or incineration is believed to render non-toxic, gently absorbable, adaptable and digestible properties to the mineral compounds. The present study characterized CS and also evaluated its immunostimulatory potential. CS was characterized by using transmission electron microscopy (TEM), X-ray powder diffraction, atomic absorption spectroscopy and CHNS analysis. The characterized CS was further evaluated for its immunomodulatory potential in Swiss mice. X-Ray diffraction analysis revealed that the CS contained silicates of magnesium, calcium and iron as major minerals. Elemental composition and heavy metal analyses showed a presence of various inorganic elements/heavy metals, albeit at levels well below daily permissive intake values. TEM analysis of the test CS revealed a presence of nano particles with an average size of 10-20 nm (≈ 26% of total material). Oral administration of CS to mice at 50, 75, 100 or 200 μg/kg body weight for 10 days led to enhanced levels of total IgG, IgG1, IgG2a and IgG2b in ovalbumin-immunized mice as well as ex vivo lymphocyte proliferation and levels of TH1 (IL-2, IFNγ) and TH2 (IL-4, IL-10) cytokines produced by their cultured splenocytes. Similarly, CS treatment resulted in enhanced delayed-type hypersensitivity responses in GRBC-primed hosts. CS also activated host peritoneal macrophages, as indicated by increases in phagocytic activity and in TLR-2, CD80 and CD86 expression. The CS did not affect liver, kidney and spleen histology. Taken together, the results indicated that absorbed CS was stimulatory of host cell-mediated immune responses. It is hypothesized for now that the immunomodulatory effect of CS may have been due, in part, to a presence of nanoparticles on the CS; further study is required to validate this viewpoint.

Ecological risk assessment of silicon dioxide nanoparticles in a freshwater fish Labeo rohita: Hematology, ionoregulation and gill Na(+)/K(+) ATPase activity

The fate and effect of nanomaterials in the environment has raised concern about their environmental risk to aquatic organisms. Silica nanoparticles (SiO2-NPs) find its uses in various fields and are inevitably released into the environment. However, the ecotoxicological effects of SiO2-NPs on the freshwater fish remain poorly understood. The aim of this study was to evaluate the effect of different concentrations (1, 5 and 25mgL(-1)) of SiO2-NPs on certain hematological, ionoregulatory and enzymological profiles of a freshwater teleost fish Labeo rohita. Hematological parameters such as hemoglobin (Hb), hematocrit (Hct), red blood cells (RBC), white blood cells (WBC), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) values were altered in SiO2-NPs treated groups. Likewise, plasma electrolytes such as plasma sodium (Na(+)), potassium (K(+)) and chloride (Cl(-)) levels and Na(+)/K(+) ATPase activity in gill of SiO2-NPs treated groups were altered in all concentrations throughout the study period (96h). The alterations of these parameters were found to be dependent on dose and exposure period. The results of the present study indicate that the alterations of these parameters may relate to physiological stress system to SiO2-NPs toxicity and also demonstrate that manufactured metal oxide NPs in aquatic environment may affect the health condition of the aquatic organisms.

Mesoporous silica nanoparticles in target drug delivery system: A review

Due to lack of specification and solubility of drug molecules, patients have to take high doses of the drug to achieve the desired therapeutic effects for the treatment of diseases. To solve these problems, there are various drug carriers present in the pharmaceuticals, which can used to deliver therapeutic agents to the target site in the body. Mesoporous silica materials become known as a promising candidate that can overcome above problems and produce effects in a controllable and sustainable manner. In particular, mesoporous silica nanoparticles (MSNs) are widely used as a delivery reagent because silica possesses favorable chemical properties, thermal stability, and biocompatibility. The unique mesoporous structure of silica facilitates effective loading of drugs and their subsequent controlled release of the target site. The properties of mesoporous, including pore size, high drug loading, and porosity as well as the surface properties, can be altered depending on additives used to prepare MSNs. Active surface enables functionalization to changed surface properties and link therapeutic molecules. They are used as widely in the field of diagnosis, target drug delivery, bio-sensing, cellular uptake, etc., in the bio-medical field. This review aims to present the state of knowledge of silica containing mesoporous nanoparticles and specific application in various biomedical fields.

Approach to using mechanism-based structure activity relationship (SAR) analysis to assess human health hazard potential of nanomaterials

With the increasing use and development of engineered nanoparticles in electronics, consumer products, pesticides, food and pharmaceutical industries, there is a growing concern about potential human health hazards of these materials. A number of studies have demonstrated that nanoparticle toxicity is extremely complex, and that the biological activity of nanoparticles will depend on a variety of physicochemical properties such as particle size, shape, agglomeration state, crystal structure, chemical composition, surface area and surface properties. Nanoparticle toxicity can be attributed to nonspecific interaction with biological structures due to their physical properties (e.g., size and shape) and biopersistence, or to specific interaction with biomolecules through their surface properties (e.g., surface chemistry and reactivity) or release of toxic ions. The toxic effects of most nanomaterials have not been adequately characterized and currently, there are many issues and challenges in toxicity testing and risk assessment of nanoparticles. Based on the possible mechanisms of action and available in vitro and in vivo toxicity database, this paper proposes an approach to using mechanism-based SAR analysis to assess the relative human health hazard/risk potential of various types of nanomaterials.

Comparative assessment of nanomaterial definitions and safety evaluation considerations

Nanomaterials continue to bring promising advances to science and technology. In concert have come calls for increased regulatory oversight to ensure their appropriate identification and evaluation, which has led to extensive discussions about nanomaterial definitions. Numerous nanomaterial definitions have been proposed by government, industry, and standards organizations. We conducted a comprehensive comparative assessment of existing nanomaterial definitions put forward by governments to highlight their similarities and differences. We found that the size limits used in different definitions were inconsistent, as were considerations of other elements, including agglomerates and aggregates, distributional thresholds, novel properties, and solubility. Other important differences included consideration of number size distributions versus weight distributions and natural versus intentionally-manufactured materials. Overall, the definitions we compared were not in alignment, which may lead to inconsistent identification and evaluation of nanomaterials and could have adverse impacts on commerce and public perceptions of nanotechnology. We recommend a set of considerations that future discussions of nanomaterial definitions should consider for describing materials and assessing their potential for health and environmental impacts using risk-based approaches within existing assessment frameworks. Our intent is to initiate a dialogue aimed at achieving greater clarity in identifying those nanomaterials that may require additional evaluation, not to propose a formal definition.

Prenatal toxicity of synthetic amorphous silica nanomaterial in rats

Synthetic amorphous silica is a nanostructured material, which is produced and used in a wide variety of technological applications and consumer products. No regulatory prenatal toxicity studies with this substance were reported yet. Therefore, synthetic amorphous silica was tested for prenatal toxicity, according to OECD guideline 414 in Wistar rats following oral (gavage) administration at the dose levels 0, 100, 300, or 1000mg/kg bw/d from gestation day 6-19. At gestation day 20, all pregnant animals were examined by cesarean section. Numbers of corpora lutea, implantations, resorptions, live and dead fetuses were counted. Fetal and placental weights were determined. Fetuses were examined for external, visceral and skeletal abnormalities. No maternal toxicity was observed at any dose level. Likewise, administration of the test compound did not alter cesarean section parameters and did not influence fetal or placental weights. No compound-related increase in the incidence of malformations or variations was observed in the fetuses. The no observed adverse effect level (NOAEL) was 1000mg/kg bw/d.

A decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping)

The European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) 'Nano Task Force' proposes a Decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping) that consists of 3 tiers to assign nanomaterials to 4 main groups, to perform sub-grouping within the main groups and to determine and refine specific information needs. The DF4nanoGrouping covers all relevant aspects of a nanomaterial's life cycle and biological pathways, i.e. intrinsic material and system-dependent properties, biopersistence, uptake and biodistribution, cellular and apical toxic effects. Use (including manufacture), release and route of exposure are applied as 'qualifiers' within the DF4nanoGrouping to determine if, e.g. nanomaterials cannot be released from a product matrix, which may justify the waiving of testing. The four main groups encompass (1) soluble nanomaterials, (2) biopersistent high aspect ratio nanomaterials, (3) passive nanomaterials, and (4) active nanomaterials. The DF4nanoGrouping aims to group nanomaterials by their specific mode-of-action that results in an apical toxic effect. This is eventually directed by a nanomaterial's intrinsic properties. However, since the exact correlation of intrinsic material properties and apical toxic effect is not yet established, the DF4nanoGrouping uses the 'functionality' of nanomaterials for grouping rather than relying on intrinsic material properties alone. Such functionalities include system-dependent material properties (such as dissolution rate in biologically relevant media), bio-physical interactions, in vitro effects and release and exposure. The DF4nanoGrouping is a hazard and risk assessment tool that applies modern toxicology and contributes to the sustainable development of nanotechnological products. It ensures that no studies are performed that do not provide crucial data and therefore saves animals and resources.

Oral two-generation reproduction toxicity study with NM-200 synthetic amorphous silica in Wistar rats

Synthetic amorphous silica (SAS) like NM-200 is used in a wide variety of technological applications and consumer products. Although SAS has been widely investigated the available reproductive toxicity studies are old and do not cover all requirements of current OECD Guidelines. As part of a CEFIC-LRI project, NM-200 was tested in a two-generation reproduction toxicity study according to OECD guideline 416. Male and female rats were treated by oral gavage with NM-200 at dose levels of 0, 100, 300 and 1000mg/kg bw/day for two generations. Body weight and food consumption were measured throughout the study. Reproductive and developmental parameters were measured and at sacrifice (reproductive) organs and tissues were sampled for histopathological analysis. Oral administration of NM-200 up to 1000mg/kg bw/day had no adverse effects on the reproductive performance of rats or on the growth and development of the offspring into adulthood for two consecutive generations. The NOAEL was 1000mg/kg body weight per day.

Aberrant cytokinesis and cell fusion result in multinucleation in HepG2 cells exposed to silica nanoparticles

The multinucleation effect of silica nanoparticles (SiNPs) had been determined in our previous studies, but the relative mechanisms of multinucleation and how the multinucleated cells are generated were still not clear. This extensional study was conducted to investigate the mechanisms underlying the formation of multinucleated cells after SiNPs exposure. We first investigated cellular multinucleation, then performed time-lapse confocal imaging to certify whether the multinucleated cells resulted from cell fusion or abnormal cell division. Our results confirmed for the first time that there are three patterns contributing to the SiNPs-induced multinucleation in HepG2 cells: cell fusion, karyokinesis without cytokinesis, and cytokinesis followed by fusion. The chromosomal passenger complex (CPC) deficiency and cell cycle arrest in G1/S and G2/M checkpoints may be responsible for the cell aberrant cytokinesis. The activated MAPK/ERK1/2 signaling and decreased mitosis related proteins might be the underlying mechanism of cell cycle arrest and thus multinucleation. In summary, we confirmed the hypothesis that aberrant cytokinesis and cell fusion resulted in multinucleation in HepG2 cells after SiNPs exposure. Since cell fusion and multinucleation were involved in genetic instability and tumor development, this study suggests the potential ability of SiNPs to induce cellular genetic instability. These findings raise concerns with regard to human health hazards and environmental risks with SiNPs exposure.

Cytotoxic and genotoxic evaluation of different synthetic amorphous silica nanomaterials in the V79 cell line

The nature of occupational risks and hazards in industries that produce or use synthetic amorphous silica (SAS) nanoparticles is still under discussion. Manufactured SAS occur in amorphous form and can be divided into two main types according to the production process, namely, pyrogenic silica (powder) and precipitated silica (powder, gel or colloid). The physical and chemical properties of SAS may vary in terms of particle size, surface area, agglomeration state or purity, and differences in their toxicity potential might therefore be expected. The aim of this study was to compare the cytotoxicity and genotoxicity of representative manufactured SAS samples in Chinese hamster lung fibroblasts (V79 cells). Five samples from industrial SAS producers were evaluated, that is, two pyrogenic SAS powders (with primary particle sizes of 20 nm and 25/70 nm), one precipitated SAS powder (20 nm) and two precipitated SAS colloids (15 and 40/80 nm). V79 cell cultures were treated with different concentrations of SAS pre-dispersed in bovine serum albumin -water medium. Pyr (pyrogenic) 20, Pre (precipitated) 20 and Col (colloid) 15 significantly decreased the cell viability after 24 h of exposure, whilst Pyr 25/70 and Col 40/80 had negligible effects. The cytotoxicity of Pyr 20, Pre 20 and Col 15 was revealed by the induction of apoptosis, and Pyr 20 and Col 15 also produced DNA damage. However, none of the SAS samples generated intracellular reactive oxidative species, micronuclei or genomic mutations in V79 cells after 24 h of exposure. Overall, the results of this study show that pyrogenic, precipitated and colloidal manufactured SAS of around 20 nm primary particle size can produce significant cytotoxic and genotoxic effects in V79 cells. In contrast, the coarser-grained pyrogenic and colloid SAS (approximately 50 nm) yielded negligible toxicity, despite having been manufactured by same processes as their finer-grained equivalents. To explain these differences, the influence of particle agglomeration and oxidative species formation is discussed.

Silica nanoparticles induce oxidative stress, inflammation, and endothelial dysfunction in vitro via activation of the MAPK/Nrf2 pathway and nuclear factor-κB signaling

Despite the widespread application of silica nanoparticles (SiNPs) in industrial, commercial, and biomedical fields, their response to human cells has not been fully elucidated. Overall, little is known about the toxicological effects of SiNPs on the cardiovascular system. In this study, SiNPs with a 58 nm diameter were used to study their interaction with human umbilical vein endothelial cells (HUVECs). Dose- and time-dependent decrease in cell viability and damage on cell plasma-membrane integrity showed the cytotoxic potential of the SiNPs. SiNPs were found to induce oxidative stress, as evidenced by the significant elevation of reactive oxygen species generation and malondialdehyde production and downregulated activity in glutathione peroxidase. SiNPs also stimulated release of cytoprotective nitric oxide (NO) and upregulated inducible nitric oxide synthase (NOS) messenger ribonucleic acid, while downregulating endothelial NOS and ET-1 messenger ribonucleic acid, suggesting that SiNPs disturbed the NO/NOS system. SiNP-induced oxidative stress and NO/NOS imbalance resulted in endothelial dysfunction. SiNPs induced inflammation characterized by the upregulation of key inflammatory mediators, including IL-1β, IL-6, IL-8, TNFα, ICAM-1, VCAM-1, and MCP-1. In addition, SiNPs triggered the activation of the Nrf2-mediated antioxidant system, as evidenced by the induction of nuclear factor-κB and MAPK pathway activation. Our findings demonstrated that SiNPs could induce oxidative stress, inflammation, and NO/NOS system imbalance, and eventually lead to endothelial dysfunction via activation of the MAPK/Nrf2 pathway and nuclear factor-κB signaling. This study indicated a potential deleterious effect of SiNPs on the vascular endothelium, which warrants more careful assessment of SiNPs before their application.