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...

Two widely used in vitro cell culture models, human liver HepG2 cells and human colon Caco2 cells, and flow cytometry techniques were evaluated as tools for rapid screening of potential genotoxicity of food-related nanosilver. Comparative genotoxic potential of 20 nm silver was evaluated in HepG2 and Caco2 cell cultures by a flow cytometric-based in vitro micronucleus assay. The nanosilver, characterized by the dynamic light scattering, transmission electron microscopy and inductively coupled plasma-mass spectrometry analysis, showed no agglomeration of the silver nanoparticles. The inductively coupled plasma-mass spectrometry and transmission electron microscopy analysis demonstrated the uptake of 20 nm silver by both cell types. The 20 nm silver exposure of HepG2 cells increased the concentration-dependent micronucleus formation sevenfold at 10 µg ml(-1) concentration in attached cell conditions and 1.3-fold in cell suspension conditions compared to the vehicle controls. However, compared to the vehicle controls, the 20 nm silver exposure of Caco2 cells increased the micronucleus formation 1.2-fold at a concentration of 10 µg ml(-1) both in the attached cell conditions as well as in the cell suspension conditions. Our results of flow cytometric in vitro micronucleus assay appear to suggest that the HepG2 cells are more susceptible to the nanosilver-induced micronucleus formation than the Caco2 cells compared to the vehicle controls. However, our results also suggest that the widely used in vitro models, HepG2 and Caco2 cells and the flow cytometric in vitro micronucleus assay are valuable tools for the rapid screening of genotoxic potential of nanosilver and deserve more careful evaluation.

The increased use of silver nanoparticles (AgNPs) in foods and cosmetics has raised public safety concerns. However, only limited knowledge exists on the effect of AgNPs on the cellular transcriptome. This study evaluated global gene expression profiles of human liver HepG2 cells exposed to 20 and 50 nm AgNPs for 4 and 24 h at 2.5 µg ml(-1) . Exposure to 20 nm AgNPs resulted in 811 altered genes after 4 h, but much less after 24 h. Exposure to 50 nm AgNPs showed minimal altered genes at both exposure times. The HepG2 cells responded to the toxic insult of AgNPs by transiently upregulating stress response genes such as metallothioneins and heat shock proteins. Functional analysis of the altered genes showed more than 20 major biological processes were affected, of which metabolism, development, cell differentiation and cell death were the most dominant categories. Several cellular pathways were also impacted by AgNP exposure, including the p53 signaling pathway and the NRF2-mediated oxidative stress response pathway, which may lead to increased oxidative stress and DNA damage in the cell and potentially result in genotoxicity and carcinogenicity. Together, these results indicate that HepG2 cells underwent a multitude of cellular processes in response to the toxic insult of AgNP exposure, and suggest that toxicogenomic characterization of human HepG2 cells could serve as an alternative model for assessing toxicities of NPs.

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.

Coumarin is widely used as a fragrance in cosmetics, perfumes and soaps. The Food and Drug Administration banned coumarin use in food because of reports that coumarin produced hepatotoxicity in rodents. Concerns about coumarin's safety have also been raised by toxicity testing conducted by the National Toxicology Program. Therefore, we initiated studies to measure the extent of coumarin absorption and metabolism in skin. [14C]Coumarin (ca. 0.5 μCi per cell) absorption in skin was measured by using two vehicles: ethanol (15 μl cm−2) and an oil‐in‐water emulsion (3 mg cm−2). Absorption was determined for 24 h by using flow‐through diffusion cells (0.64 cm2, exposed skin) with a receptor fluid consisting of HEPES‐buffered Hank's balanced salt solution (pH 7.4). Coumarin metabolism was determined by high‐performance liquid chromatography methodology. In rat skin (n = 3), the percentages of applied dose absorbed after 24 h were 54.9 ± 0.63 (mean ± SEM) and 86.8 ± 5.4 for the ethanol and emulsion vehicles, respectively, with ca. 5% remaining in skin. In human skin (n = 2), the percentages of applied dose absorbed after 24 h were 64.4 ± 0.29 and 98.0 ± 5.3 for the ethanol and emulsion vehicles, respectively, with ca. 1% remaining in skin. The extent of skin absorption was greater from the emulsion vehicle than from the ethanol vehicle in both human and rat skin. Coumarin rapidly penetrated both rat and human skin with >75% and >95%, respectively, of the absorbed dose found in the receptor fluid within 6 h. No evidence of coumarin metabolism was found in either skin or receptor fluid fractions. These studies indicate that coumarin absorption is significant in skin. Systemic coumarin absorption must be expected after dermal contact with coumarin‐containing products. © 1997 John Wiley & Sons, Ltd.

I Although the majority of deaths resulting from exposure to sulfur mustard (HD) have been due to pulmonary dysfunction, there are no detailed accounts of the pathogenesis of HDinduced lesions in the respiratory tract. Accordingly, we investigated the early changes within the trachea and lungs of rats following inhalation exposure to HD. Anesthetized rats were exposed by intratracheal intubation to vaporized H D (0.35 mg in 100 wl absolute ethanol) or ethanol alone for 50 min. Animals were euthanatized at 0, 1, 4, 6, 12, 18, and 24 li postexposure (PE), and their respiratory tracts were prepared for histological and ultrastructural examination. In rats exposed to HD, multifocal, petechial hemorrhages were grossly evident on tlie pleural surface of the lung at 6 h PE. Atelectasis and edema of the accessory lobe occurred at 12-18 h PE. Histologically, lesions in the respiratory tract were confined primarify to the trachea, bronchi and targer bronchioles. It, HD-exposed rats, there was a progressive depletion of the bronchiolar-associated lymphoid tissue (BALTI, with necrosis of the lymphoid cells as early as 12 h PE. Necrosis and sloughing of the tracheal and bronchial epithelia at 6-12 h PE was followed by the formation of fibrinous pseudomembranes within the bronchi. Necrosis and separation of airway epithelia occurred at the mucosaUsubmucosal interface. Pseudomembranes formed almost exclusively in deepitlielialized areas overlying tlie BALT. Cartilaginous lesions, characterized by necrosis of individual chondrocytes, were evident at I2 li PE. Pulmonary edema and occasional alveolar hemorrhage occurred from I8 to 24 li PE. Small bronchioles and alveoli were relatively unaffected, and only a few inflammatory cells were observed at any time.

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