Influence of simulated gastrointestinal conditions on particle-induced cytotoxicity and interleukin-8 regulation in differentiated and undifferentiated Caco-2 cells

Low uptake of silica nanoparticles in Caco-2 intestinal epithelial barriers

Cellular barriers, such as the skin, the lung epithelium or the intestinal epithelium, constitute one of the first obstacles facing nanomedicines or other nanoparticles entering organisms. It is thus important to assess the capacity of nanoparticles to enter and transport across such barriers. In this work, Caco-2 intestinal epithelial cells were used as a well-established model for the intestinal barrier, and the uptake, trafficking and translocation of model silica nanoparticles of different sizes were investigated using a combination of imaging, flow cytometry and transport studies. Compared to typical observations in standard cell lines commonly used for in vitro studies, silica nanoparticle uptake into well-developed Caco-2 cellular barriers was found to be very low. Instead, nanoparticle association to the apical outer membrane was substantial and these particles could easily be misinterpreted as internalised in the absence of imaging. Passage of nanoparticles through the barrier was very limited, suggesting that the low amount of internalised nanoparticles was due to reduced uptake into cells, rather than a considerable transport through them.

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.

In vitro toxicity assessment of oral nanocarriers

The fascinating properties of nanomaterials opened new frontiers in medicine. Nanocarriers are useful systems in transporting drugs to site-specific targets. The unique physico-chemical characteristics making nanocarriers promising devices to treat diseases may also be responsible for potential adverse effects. In order to develop functional nano-based drug delivery systems, efficacy and safety should be carefully evaluated. To date, no common testing strategy to address nanomaterial toxicological challenges has been generated. Different cell culture models are currently used to evaluate nanocarrier safety using conventional in vitro assays, but overall they have generated a huge amount of conflicting data. In this review we describe state-of-the-art approaches for in vitro testing of orally administered nanocarriers, highlighting the importance of developing harmonized and validated standard operating procedures. These procedures should be applied in a safe-by-design context with the aim to reduce and/or eliminate the uncertainties and risks associated with nanomedicine development.

The Role of the Food Matrix and Gastrointestinal Tract in the assessment of biological properties of ingested engineered nanomaterials (iENMs): State of the science and knowledge gaps

Many foods contain appreciable levels of engineered nanomaterials (ENMs) (diameter < 100 nm) that may be either intentionally or unintentionally added. These ENMs vary considerably in their compositions, dimensions, morphologies, physicochemical properties, and biological responses. From a toxicological point of view, it is often convenient to classify ingested ENMs (iENMs) as being either inorganic (such as TiO₂, SiO₂, Fe₂O₃, or Ag) or organic (such as lipid, protein, or carbohydrate), since the former tend to be indigestible and the latter are generally digestible. At present there is a relatively poor understanding of how different types of iENMs behave within the human gastrointestinal tract (GIT), and how the food matrix and biopolymers transform their physico-chemical properties and influence their gastrointestinal fate. This lack of knowledge confounds an understanding of their potential harmful effects on human health. The purpose of this article is to review our current understanding of the GIT fate of iENMs, and to highlight gaps where further research is urgently needed in assessing potential risks and toxicological implications of iENMs. In particular, a strong emphasis is given to the development of standardized screening methods that can be used to rapidly and accurately assess the toxicological properties of iENMs.

Titanium Dioxide Particle Type and Concentration Influence the Inflammatory Response in Caco-2 Cells

Titanium dioxide (TiO₂) nanoparticles are widely used in cosmetics, sunscreens, biomedicine, and food products. When used as a food additive, TiO₂ nanoparticles are used in significant amounts as white food-coloring agents. However, the effects of TiO₂ nanoparticles on the gastrointestinal tract remain unclear. The present study was designed to determine the effects of five TiO₂ particles of different crystal structures and sizes in human epithelial colorectal adenocarcinoma (Caco-2) cells and THP-1 monocyte-derived macrophages. Twenty-four-hour exposure to anatase (primary particle size: 50 and 100 nm) and rutile (50 nm) TiO₂ particles reduced cellular viability in a dose-dependent manner in THP-1 macrophages, but in not Caco-2 cells. However, 72-h exposure of Caco-2 cells to anatase (50 nm) TiO₂ particles reduced cellular viability in a dose-dependent manner. The highest dose (50 µg/mL) of anatase (100 nm), rutile (50 nm), and P25 TiO₂ particles also reduced cellular viability in Caco-2 cells. The production of reactive oxygen species tended to increase in both types of cells, irrespective of the type of TiO₂ particle. Exposure of THP-1 macrophages to 50 µg/mL of anatase (50 nm) TiO₂ particles increased interleukin (IL)-1β expression level, and exposure of Caco-2 cells to 50 µg/mL of anatase (50 nm) TiO₂ particles also increased IL-8 expression. The results indicated that anatase TiO₂ nanoparticles induced inflammatory responses compared with other TiO₂ particles. Further studies are required to determine the in vivo relevance of these findings to avoid the hazards of ingested particles.

Cytotoxicity of Nanoparticles Contained in Food on Intestinal Cells and the Gut Microbiota

Toxicity of nanoparticles (NPs) upon oral exposure has been studied in animals using physiological changes, behavior, histology, and blood analysis for evaluation. The effects recorded include the combination of the action on cells of the exposed animal and the reaction of the microorganisms that populate the external and internal surfaces of the body. The importance of these microorganisms, collectively termed as microbiota, for the health of the host has been widely recognized. They may also influence toxicity of NPs but these effects are difficult to differentiate from toxicity on cells of the gastrointestinal tract. To estimate the likelihood of preferential damage of the microbiota by NPs the relative sensitivity of enterocytes and bacteria was compared. For this comparison NPs with antimicrobial action present in consumer products were chosen. The comparison of cytotoxicity with Escherichia coli as representative for intestinal bacteria and on gastrointestinal cells revealed that silver NPs damaged bacteria at lower concentrations than enterocytes, while the opposite was true for zinc oxide NPs. These results indicate that silver NPs may cause adverse effects by selectively affecting the gut microbiota. Fecal transplantation from NP-exposed animals to unexposed ones offers the possibility to verify this hypothesis.

Immune response elicited by an intranasally delivered HBsAg low-dose adsorbed to poly-ε-caprolactone based nanoparticles

Among new strategies to increase hepatitis B virus (HBV) vaccination, especially in developing countries, the development of self-administered vaccines is considered one of the most valuable. Nasal vaccination using polymeric nanoparticles (NPs) constitutes a valid approach to this issue. In detail, poly-ε-caprolactone (PCL)/chitosan NPs present advantages as a mucosal vaccine delivery system: the high resistance of PCL against degradation in biological fluids and the mucoadhesive and immunostimulatory properties of chitosan. In vitro studies revealed these NPs were retained in a mucus-secreting pulmonary epithelial cell line and were capable of entering into differentiated epithelial cells. The intranasal (IN) administration of 3 different doses of HBsAg (1.5 μg, 5 μg and 10 μg) adsorbed on a fixed amount of PCL/chitosan NPs (1614 μg) generated identical titers of serum anti-HBsAg IgG and anti-HBsAg sIgA in mice nasal secretions. Besides other factors, the NP surface characteristics, particularly, zeta potential differences among the administered formulations are believed to be implicated in the outcome of the immune response generated.

Effects of silver nanoparticles and ions on a co-culture model for the gastrointestinal epithelium

Background

The increased incorporation of silver nanoparticles (Ag NPs) into consumer products makes the characterization of potential risk for humans and other organisms essential. The oral route is an important uptake route for NPs, therefore the study of the gastrointestinal tract in respect to NP uptake and toxicity is very timely. The aim of the present study was to evaluate the effects of Ag NPs and ions on a Caco-2/TC7:HT29-MTX intestinal co-culture model with mucus secretion, which constitutes an important protective barrier to exogenous agents in vivo and may strongly influence particle uptake.

Methods

The presence of the mucus layer was confirmed with staining techniques (alcian blue and toluidine blue). Mono and co-cultures of Caco-2/TC7 and HT29-MTX cells were exposed to Ag NPs (Ag 20 and 200 nm) and AgNO₃ and viability (alamar blue), ROS induction (DCFH-DA assay) and IL-8 release (ELISA) were measured. The particle agglomeration in the media was evaluated with DLS and the ion release with ultrafiltration and ICP-MS. The effects of the Ag NPs and AgNO₃ on cells in co-culture were studied at a proteome level with two-dimensional difference in gel electrophoresis (2D-DIGE) followed by Matrix Assisted Laser Desorption Ionization - Time Of Flight/ Time Of Flight (MALDI-TOF/TOF) mass spectrometry (MS). Intracellular localization was assessed with NanoSIMS and TEM.

Results

The presence of mucus layer led to protection against ROS and decrease in IL-8 release. Both Ag 20 and 200 nm NPs were taken up by the cells and Ag NPs 20 nm were mainly localized in organelles with high sulfur content. A dose- and size-dependent increase in IL-8 release was observed with a lack of cytotoxicity and oxidative stress. Sixty one differentially abundant proteins were identified involved in cytoskeleton arrangement and cell cycle, oxidative stress, apoptosis, metabolism/detoxification and stress.

Conclusions

The presence of mucus layer had an impact on modulating the induced toxicity of NPs. NP-specific effects were observed for uptake, pro-inflammatory response and changes at the proteome level. The low level of overlap between differentially abundant proteins observed in both Ag NPs and AgNO₃ treated co-culture suggests size-dependent responses that cannot only be attributed to soluble Ag.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0117-9) contains supplementary material, which is available to authorized users.

Altered global gene expression profiles in human gastrointestinal epithelial Caco2 cells exposed to nanosilver

Extensive consumer exposure to food- and cosmetics-related consumer products containing nanosilver is of public safety concern. Therefore, there is a need for suitable in vitro models and sensitive predictive rapid screening methods to assess their toxicity. Toxicogenomic profile showing subtle changes in gene expressions following nanosilver exposure is a sensitive toxicological endpoint for this purpose. We evaluated the Caco2 cells and global gene expression profiles as tools for predictive rapid toxicity screening of nanosilver. We evaluated and compared the gene expression profiles of Caco-2 cells exposed to 20 nm and 50 nm nanosilver at a concentration 2.5 μg/ml. The global gene expression analysis of Caco2 cells exposed to 20 nm nanosilver showed that a total of 93 genes were altered at 4 h exposure, out of which 90 genes were up-regulated and 3 genes were down-regulated. The 24 h exposure of 20 nm silver altered 15 genes in Caco2 cells, out of which 14 were up-regulated and one was down-regulated. The most pronounced changes in gene expression were detected at 4 h. The greater size (50 nm) nanosilver at 4 h exposure altered more genes by more different pathways than the smaller (20 nm) one. Metallothioneins and heat shock proteins were highly up-regulated as a result of exposure to both the nanosilvers. The cellular pathways affected by the nanosilver exposure is likely to lead to increased toxicity. The results of our study presented here suggest that the toxicogenomic characterization of Caco2 cells is a valuable in vitro tool for assessing toxicity of nanomaterials such as nanosilver.

'Bio-nano interactions: new tools, insights and impacts': summary of the Royal Society discussion meeting

Bio-nano interactions can be defined as the study of interactions between nanoscale entities and biological systems such as, but not limited to, peptides, proteins, lipids, DNA and other biomolecules, cells and cellular receptors and organisms including humans. Studying bio-nano interactions is particularly useful for understanding engineered materials that have at least one dimension in the nanoscale. Such materials may consist of discrete particles or nanostructured surfaces. Much of biology functions at the nanoscale; therefore, our ability to manipulate materials such that they are taken up at the nanoscale, and engage biological machinery in a designed and purposeful manner, opens new vistas for more efficient diagnostics, therapeutics (treatments) and tissue regeneration, so-called nanomedicine. Additionally, this ability of nanomaterials to interact with and be taken up by cells allows nanomaterials to be used as probes and tools to advance our understanding of cellular functioning. Yet, as a new technology, assessment of the safety of nanomaterials, and the applicability of existing regulatory frameworks for nanomaterials must be investigated in parallel with development of novel applications. The Royal Society meeting 'Bio-nano interactions: new tools, insights and impacts' provided an important platform for open dialogue on the current state of knowledge on these issues, bringing together scientists, industry, regulatory and legal experts to concretize existing discourse in science law and policy. This paper summarizes these discussions and the insights that emerged.

Physicochemical and toxicological evaluation of silica nanoparticles suitable for food and consumer products collected by following the EC recommendation

Specific information about the particle size distribution, agglomeration state, morphology, and chemical composition of four silica samples, used as additives in food and in personal care products, were achieved with a combination of analytical techniques. The combined use of differential centrifugal sedimentation (DCS), sedimentation field flow fractionation (SdFFF), and scanning and transmission electron microscopy (SEM and TEM) allows to classify the water dispersed samples as "nanomaterials" according to the EC definition. The mechanical stirring and the ultrasound treatment were compared as dispersion methods. The particle surface chemical composition, determined by particle-induced X-ray emission (PIXE) and X-ray photoelectron spectroscopy (XPS), assessed the different levels of purity between the pyrogenic and the precipitated silica and highlighted particle surface chemical composition modifications in the outer shell when dispersed by mechanical stirring. The potential toxic effects of silica on intestinal Caco-2 cells were investigated using MTS assay and by measuring lactate dehydrogenase (LDH) release and caspases 3/7 activity after 24 h of incubation. No or limited decrease of cell viability was observed for all particles regardless of dispersion procedure, suggesting a relative innocuity of these silica samples.

In vitro gastrointestinal digestion increases the translocation of polystyrene nanoparticles in an in vitro intestinal co-culture model

The conditions of the gastrointestinal tract may change the physicochemical properties of nanoparticles (NPs) and therewith the bioavailability of orally taken NPs. Therefore, we assessed the impact of in vitro gastrointestinal digestion on the protein corona of polystyrene NPs (PS-NPs) and their subsequent translocation across an in vitro intestinal barrier. A co-culture of intestinal Caco-2 and HT29-MTX cells was exposed to 50 nm PS-NPs of different charges (positive and negative) in two forms: pristine and digested in an in vitro gastrointestinal digestion model. In vitro digestion significantly increased the translocation of all, except the "neutral", PS-NPs. Upon in vitro digestion, translocation was 4-fold higher for positively charged NPs and 80- and 1.7-fold higher for two types of negatively charged NPs. Digestion significantly reduced the amount of protein in the corona of three out of four types of NPs. This reduction of proteins was 4.8-fold for "neutral", 3.5-fold for positively charged and 1.8-fold for one type of negatively charged PS-NPs. In vitro digestion also affected the composition of the protein corona of PS-NPs by decreasing the presence of higher molecular weight proteins and shifting the protein content of the corona to low molecular weight proteins. These findings are the first to report that in vitro gastrointestinal digestion significantly affects the protein corona and significantly increases the in vitro translocation of differently charged PS-NPs. These findings stress the importance of including the in vitro digestion in future in vitro intestinal translocation screening studies for risk assessment of orally taken NPs.

Nanomaterials in consumer products: a challenging analytical problem

Many products used in everyday life are made with the assistance of nanotechnologies. Cosmetic, pharmaceuticals, sunscreen, powdered food are only few examples of end products containing nano-sized particles (NPs), generally added to improve the product quality. To evaluate correctly benefits vs. risks of engineered nanomaterials and consequently to legislate in favor of consumer's protection, it is necessary to know the hazards connected with the exposure levels. This information implies transversal studies and a number of different competences. On analytical point of view the identification, quantification and characterization of NPs in food matrices and in cosmetic or personal care products pose significant challenges, because NPs are usually present at low concentration levels and the matrices, in which they are dispersed, are complexes and often incompatible with analytical instruments that would be required for their detection and characterization. This paper focused on some analytical techniques suitable for the detection, characterization and quantification of NPs in food and cosmetics products, reports their recent application in characterizing specific metal and metal-oxide NPs in these two important industrial and market sectors. The need of a characterization of the NPs as much as possible complete, matching complementary information about different metrics, possible achieved through validate procedures, is what clearly emerges from this research. More work should be done to produce standardized materials and to set-up methodologies to determine number-based size distributions and to get quantitative date about the NPs in such a complex matrices.

Mechanism of neutrophil activation and toxicity elicited by engineered nanomaterials

The effects of nanomaterials (NMs) on biological systems, especially their ability to stimulate inflammatory responses requires urgent investigation. We evaluated the response of the human differentiated HL60 neutrophil-like cell line to NMs. It was hypothesised that NM physico-chemical characteristics would influence cell responsiveness by altering intracellular Ca2+ concentration [Ca2+]i and reactive oxygen species production. Cells were exposed (1.95-125 μg/ml, 24 h) to silver (Ag), zinc oxide (ZnO), titanium dioxide (TiO2), multi-walled carbon nanotubes (MWCNTs) or ultrafine carbon black (ufCB) and cytotoxicity assessed (alamar blue assay). Relatively low (TiO2, MWCNTs, ufCB) or high (Ag, ZnO) cytotoxicity NMs were identified. Sub-lethal impacts of NMs on cell function were investigated for selected NMs only, namely TiO2, Ag and ufCB. Only Ag stimulated cell activation. Within minutes, Ag stimulated an increase in [Ca2+]i (in Fura-2 loaded cells), and a prominent inward ion current (assessed by electrophysiology). Within 2-4 h, Ag increased superoxide anion release and stimulated cytokine production (MCP-1, IL-8) that was diminished by Ca2+ inhibitors or trolox. Light microscopy demonstrated that cells had an activated phenotype. In conclusion NM toxicity was ranked; Ag>ufCB>TiO2, and the battery of tests used provided insight into the mechanism of action of NM toxicity to guide future testing strategies.

The protein corona protects against size- and dose-dependent toxicity of amorphous silica nanoparticles

Besides the lung and skin, the gastrointestinal (GI) tract is one of the main targets for accidental exposure or biomedical applications of nanoparticles (NP). Biological responses to NP, including nanotoxicology, are caused by the interaction of the NP with cellular membranes and/or cellular entry. Here, the physico-chemical characteristics of NP are widely discussed as critical determinants, albeit the exact mechanisms remain to be resolved. Moreover, proteins associate with NP in physiological fluids, forming the protein corona potentially transforming the biological identity of the particle and thus, adding an additional level of complexity for the bio-nano responses. Here, we employed amorphous silica nanoparticles (ASP) and epithelial GI tract Caco-2 cells as a model to study the biological impact of particle size as well as of the protein corona. Caco-2 or mucus-producing HT-29 cells were exposed to thoroughly characterized, negatively charged ASP of different size in the absence or presence of proteins. Comprehensive experimental approaches, such as quantifying cellular metabolic activity, microscopic observation of cell morphology, and high-throughput cell analysis revealed a dose- and time-dependent toxicity primarily upon exposure with ASP30 (Ø = 30 nm). Albeit smaller (ASP20, Ø = 20 nm) or larger particles (ASP100; Ø = 100 nm) showed a similar zeta potential, they both displayed only low toxicity. Importantly, the adverse effects triggered by ASP30/ASP30L were significantly ameliorated upon formation of the protein corona, which we found was efficiently established on all ASP studied. As a potential explanation, corona formation reduced ASP30 cellular uptake, which was however not significantly affected by ASP surface charge in our model. Collectively, our study uncovers an impact of ASP size as well as of the protein corona on cellular toxicity, which might be relevant for processes at the nano-bio interface in general.

Comparative genotoxicity of nanosilver in human liver HepG2 and colon Caco2 cells evaluated by fluorescent microscopy of cytochalasin B-blocked micronucleus formation

As a consequence of the increased use of silver nanoparticles in food, food contact materials, dietary supplements and cosmetics to prevent fungal and bacterial growth, there is a need for validated rapid screening methods to assess the safety of nanoparticle exposure. This study evaluated two widely used in vitro cell culture models, human liver HepG2 cells and human colon Caco2 cells, as tools for assessing the potential genotoxicity of 20-nm nanosilver. The average silver nanoparticle size as determined by transmission electron microscopy (TEM) was 20.4 nm. Dynamic light scattering (DLS) analysis showed no large agglomeration of the silver nanoparticles. The silver concentration in a 20-nm nanosilver solution determined by the inductively coupled plasma-mass spectrometry (ICP-MS) analysis was 0.962 mg ml(-1) . Analysis by ICP-MS and TEM demonstrated the uptake of 20-nm silver by both HepG2 and Caco2 cells. Genotoxicity was determined by the cytochalasin B-blocked micronucleus assay with acridine orange staining and fluorescence microscopy. Concentration- and time-dependent increases in the frequency of binucleated cells with micronuclei induced by the nanosilver was observed in the concentration range of 0.5 to 15 µg ml(-1) in both HepG2 and Caco2 cells compared with the control. Our results indicated that HepG2 cells were more sensitive than Caco2 cells in terms of micronuclei formation induced by nanosilver exposure. In summary, the results of this study indicate that the widely used in vitro models, HepG2 and Caco2 cells in culture, represent potential screening models for prediction of genotoxicity of silver nanoparticles by in vitro micronucleus assay.

Cell uptake and oral absorption of titanium dioxide nanoparticles

Large efforts are invested on the development of in vitro tests to evaluate nanomaterial (NM) toxicity. In order to assess the relevance of the adverse effects identified in in vitro toxicity tests a thorough understanding of the biokinetics of NMs is critical. We used different in vitro and in vivo test methods to evaluate cell uptake and oral absorption of titanium dioxide nanoparticles (TiO2 NPs). These NPs were readily uptaken by A549 cells (carcinomic human alveolar basal epithelial cells) in vitro. Such rapid uptake contrasted with a very low oral absorption in a differentiated Caco-2 monolayer system (human epithelial colorectal adenocarcinoma cells) and after oral gavage administration to rats. In this oral study, no significant increase in the levels of titanium was recorded by ICP-MS in any of the tissues evaluated (including among other: small intestine, Peyer's patches, mesenteric lymph nodes, liver, and spleen). No NPs were observed by TEM in sections of the small intestine, except for several particles in the cytoplasm of a cell from a Peyer's Patch area. The observation of NPs in Peyer's Patch suggests that the Caco-2 monolayer system is likely to underestimate the potential for oral absorption of NPs and that the model could be improved by including M-cells in co-culture.

Comparative cytotoxicity of nanosilver in human liver HepG2 and colon Caco2 cells in culture

The use of silver nanoparticles in food, food contact materials, dietary supplements and cosmetics has increased significantly owing to their antibacterial and antifungal properties. As a consequence, the need for validated rapid screening methods to assess their toxicity is necessary to ensure consumer safety. This study evaluated two widely used in vitro cell culture models, human liver HepG2 cells and human colon Caco2 cells, as tools for assessing the potential cytotoxicity of food- and cosmetic-related nanoparticles. The two cell culture models were utilized to compare the potential cytotoxicity of 20-nm silver. The average size of the silver nanoparticle determined by our transmission electron microscopy (TEM) analysis was 20.4 nm. The dynamic light scattering (DLS) analysis showed no large agglomeration of the silver nanoparticles. The concentration of the 20-nm silver solution determined by our inductively coupled plasma-mass spectrometry (ICP-MS) analysis was 0.962 mg ml(-1) . Our ICP-MS and TEM analysis demonstrated the uptake of 20-nm silver by both HepG2 and Caco2 cells. Cytotoxicity, determined by the Alamar Blue reduction assay, was evaluated in the nanosilver concentration range of 0.1 to 20 µg ml(-1) . Significant concentration-dependent cytotoxicity of the nanosilver in HepG2 cells was observed in the concentration range of 1 to 20 µg ml(-1) and at a higher concentration range of 10 to 20 µg ml(-1) in Caco2 cells compared with the vehicle control. A concentration-dependent decrease in dsDNA content was observed in both cell types exposed to nanosilver but not controls, suggesting an increase in DNA damage. The DNA damage was observed in the concentration range of 1 to 20 µg ml(-1) . Nanosilver-exposed HepG2 and Caco2 cells showed no cellular oxidative stress, determined by the dichlorofluorescein assay, compared with the vehicle control in the concentration range used in this study. A concentration-dependent decrease in mitochondria membrane potential in both nanosilver exposed cell types suggested increased mitochondria injury compared with the vehicle control. The mitochondrial injury in HepG2 cells was significant in the concentration range of 1 to 20 µg ml(-1) , but in Caco2 cells it was significant at a higher concentration range of 10 to 20 µg ml(-1) . These results indicated that HepG2 cells were more sensitive to nanosilver exposure than Caco2 cells. It is generally believed that cellular oxidative stress induces cytotoxicity of nanoparticles. However, in this study we did not detect any nanosilver-induced oxidative stress in either cell type at the concentration range used in this study. Our results suggest that cellular oxidative stress did not play a major role in the observed cytotoxicity of nanosilver in HepG2 and Caco2 cells and that a different mechanism of nanosilver-induced mitochondrial injury leads to the cytotoxicity. The HepG2 and Caco2 cells used this study appear to be targets for silver nanoparticles. The results of this study suggest that the differences in the mechanisms of toxicity induced by nanosilver may be largely as a consequence of the type of cells used. This differential rather than universal response of different cell types exposed to nanoparticles may play an important role in the mechanism of their toxicity. In summary, the results of this study indicate that the widely used in vitro models, HepG2 and Caco2 cells in culture, are excellent systems for screening cytotoxicity of silver nanoparticles. These long established cell culture models and simple assays used in this study can provide useful toxicity and mechanistic information that can help to better inform safety assessments of food- and cosmetic-related silver nanoparticles.

Progress in the characterization and safety evaluation of engineered inorganic nanomaterials in food

Nanotechnology has stepped into the food industry, from the farm to the table at home, in order to improve the taste and nutritional value, extend the shelf-life and monitor the food quality. In fact, as consumers we have already been in contact, via oral exposure, with a number of food products containing engineered nanomaterials (ENMs) more often than most people think. However, the fate of ENMs after entering the GI tract of the human body is not yet clearly understood. Hence, the related safety issue is raised, and attracts much attention and wide debate from the public, even including protest demonstrations against nanotechnology in food. In this review, we summarize the up-to-date information about the characterization and safety evaluation of common inorganic ENMs (with a focus on silver, titanium dioxide, silica and zinc oxide nanoparticles) in food. Based on the literature, a whole scenario of the safety issue of these ENMs in food and an outlook on the future studies are given.

Minimal intestinal epithelial cell toxicity in response to short- and long-term food-relevant inorganic nanoparticle exposure

Toxicity of commercial nanoparticles of titania, silica, and zinc oxides is being investigated in this in vitro study. Particles of these compositions are found in many food items, and thus this study is directed toward particle behavior in simulated digestion media and their interaction with intestinal epithelial cell line C2BBe1, a clone of Caco-2 cells, originally isolated from a human colon cancer. Even though the primary particle size of all three particles was below 50 nm, the particles appeared as aggregates in culture media with a negatively charged surface. In the presence of pepsin (pH 2), the charge on the titania became positive, and silica was almost neutral and aggregated extensively, whereas ZnO dissolved. For silica and titania, treatment with simulated intestinal digestive solution led to a strongly negatively charged surface and particle sizes approaching values similar to those in media. On the basis of infrared spectroscopy, we concluded that the surface of silica and titania was covered with bile salts/proteins after this treatment. Transmission electron microscopy indicated that the C2BBe1 cells internalized all three particles. Toxicity assays included investigation of necrosis, apoptosis, membrane damage, and mitochondrial activity. Titania and SiO₂ particles suspended in media at loading levels of 10 μg/cm² exhibited no toxicity. With ZnO at the same loading level, mild toxicity was observed based only on the LDH assay and decrease of mitochondrial activity and not necrosis or apoptosis. Titania particles exposed to the simulated digestion media exhibited mild toxicity based on decrease of mitochondrial activity, likely due to transport of toxic bile salts via adsorption on the particle surface.

Zinc oxide nanoparticles induce necrosis and apoptosis in macrophages in a p47phox- and Nrf2-independent manner

In view of the steadily increasing use of zinc oxide nanoparticles in various industrial and consumer applications, toxicological investigations to evaluate their safety are highly justified. We have investigated mechanisms of ZnO nanoparticle-induced apoptosis and necrosis in macrophages in relation to their important role in the clearance of inhaled particulates and the regulation of immune responses during inflammation. In the murine macrophage RAW 264.7 cell line, ZnO treatment caused a rapid induction of nuclear condensation, DNA fragmentation, and the formation of hypodiploid DNA nuclei and apoptotic bodies. The involvement of the essential effector caspase-3 in ZnO-mediated apoptosis could be demonstrated by immunocytochemical detection of activated caspase-3 in RAW 264.7 cells. ZnO specifically triggered the intrinsic apoptotic pathway, because Jurkat T lymphocytes deficient in the key mediator caspase-9 were protected against ZnO-mediated toxicity whereas reconstituted cells were not. ZnO also caused DNA strand breakage and oxidative DNA damage in the RAW 264.7 cells as well as p47(phox) NADPH oxidase-dependent superoxide generation in bone marrow-derived macrophages. However, ZnO-induced cell death was not affected in bone marrow-derived macrophages of mice deficient in p47(phox) or the oxidant responsive transcription factor Nrf2. Taken together, our data demonstrate that ZnO nanoparticles trigger p47(phox) NADPH oxidase-mediated ROS formation in macrophages, but that this is dispensable for caspase-9/3-mediated apoptosis. Execution of apoptotic cell death by ZnO nanoparticles appears to be NADPH oxidase and Nrf2-independent but rather triggered by alternative routes.