New methodological developments for testing the in vitro genotoxicity of nanomaterials: Comparison of 2D and 3D HepaRG liver cell models and classical and high throughput comet assay formats

Nanomaterials (NMs) are defined as materials with at least one external dimension below 100 nm. Their small size confers them interesting unique physico-chemical properties, hence NMs are increasingly used in a diversity of applications. However, the specific properties of NMs could also make them more harmful than their bulk counterparts. Therefore, there is a crucial need to deliver efficient NM hazard assessment in order to sustain the responsible development of nanotechnology. This study analysed the genotoxic potential of several NMs: one titanium dioxide (TiO2) and two zinc oxide NMs (ZnO) that were tested up to 100 μg/mL on 2D and 3D hepatic HepaRG models. Genotoxicity analysis was performed comparing the alkaline comet assay in classical and high throughput formats. Moreover, oxidative DNA lesions were investigated with the Fpg-modified comet assay. Results showed that TiO2 NMs were not cytotoxic and not genotoxic in either cell model, although a small increase in the % tail DNA was observed in 3D HepaRG cells at 100 μg/mL in the classical format. The two ZnO NMs (ZnO S. NMs a commercial suspension and NM110 provided by the European Union Joint Research Centre) induced a concentration-dependent increase in cytotoxicity that was more pronounced in the 2D (>20% cytotoxicity was observed for ZnO S. at concentrations greater than 25 μg/mL, and for NM 110 at 50 μg/mL) than in the 3D model (more than 20% cytotoxicity for ZnO S. NMs at 50 μg/mL). While ZnO S. NMs induced DNA damage associated with cytotoxicity (at 25 and 50 μg/mL in 2D and 50 μg/mL in 3D), NM110 showed a clear genotoxic effect at non-cytotoxic concentrations (25 μg/mL in 2D and at 25 and 50 μg/mL in 3D). No major differences could be observed in the comet assay in the presence or absence of the Fpg enzyme. High throughput analysis using CometChip® mostly confirmed the results obtained with the classical format, and even enhanced the detection of genotoxicity in the 3D model. In conclusion, this study demonstrated that new approach methodologies (NAMs), 3D models and the high throughput format for the comet assay, were more efficient in the detection of genotoxic effects, and are therefore promising approaches to improve hazard assessment of NMs.

New approach methodologies to facilitate and improve the hazard assessment of non-genotoxic carcinogens-a PARC project

Carcinogenic chemicals, or their metabolites, can be classified as genotoxic or non-genotoxic carcinogens (NGTxCs). Genotoxic compounds induce DNA damage, which can be detected by an established in vitro and in vivo battery of genotoxicity assays. For NGTxCs, DNA is not the primary target, and the possible modes of action (MoA) of NGTxCs are much more diverse than those of genotoxic compounds, and there is no specific in vitro assay for detecting NGTxCs. Therefore, the evaluation of the carcinogenic potential is still dependent on long-term studies in rodents. This 2-year bioassay, mainly applied for testing agrochemicals and pharmaceuticals, is time-consuming, costly and requires very high numbers of animals. More importantly, its relevance for human risk assessment is questionable due to the limited predictivity for human cancer risk, especially with regard to NGTxCs. Thus, there is an urgent need for a transition to new approach methodologies (NAMs), integrating human-relevant in vitro assays and in silico tools that better exploit the current knowledge of the multiple processes involved in carcinogenesis into a modern safety assessment toolbox. Here, we describe an integrative project that aims to use a variety of novel approaches to detect the carcinogenic potential of NGTxCs based on different mechanisms and pathways involved in carcinogenesis. The aim of this project is to contribute suitable assays for the safety assessment toolbox for an efficient and improved, internationally recognized hazard assessment of NGTxCs, and ultimately to contribute to reliable mechanism-based next-generation risk assessment for chemical carcinogens.

Lysophosphatidylcholine-DHA Specifically Induces Cytotoxic Effects of the MDA-MB-231 Human Breast Cancer Cell Line In Vitro-Comparative Effects with Other Lipids Containing DHA

Docosahexaenoic acid (DHA, C22:6 ω-3) is a dietary polyunsaturated fatty acid that has an important role in human health. Epidemiological studies linked a high intake of DHA to a reduced risk of certain cancers. Recently, attention focused on how the lipid carrier in which DHA is delivered, i.e., esterified on acylglycerols, phospholipids, or free, affects its biological effects. However, studies comparing the effects of these different forms for DHA supply to cancer cells in vitro are limited. In this study, the effect of free DHA and five lipids carrying one to three DHA chains (LPC-DHA, PC-DHA, MAG-DHA, DAG-DHA and TAG-DHA) on the viability of the MDA-MB-231 breast cancer cell line was compared. Our results revealed a strong structure-function relationship of DHA-carrying lipids on the viability of MDA-MB-231 cells. Glycerophosphocholine-based lipids are the most effective DHA carriers in reducing the viability of MDA-MB-231 cells, with LPC-DHA being more effective (IC₅₀ = 23.7 µM) than PC-DHA (IC₅₀ = 67 µM). The other tested lipids are less toxic (MAG-DHA, free DHA) or even not toxic (DAG-DHA, TAG-DHA) under our conditions. Investigating the mechanism of cell death induced by LPC-DHA revealed increased oxidative stress and membrane cell damage.

An Evaluation of the Cytotoxic and Genotoxic Effects of the Marine Toxin C17-SAMT in Human TK6 and HepaRG Cell Lines

This study investigates the genotoxicity and cytotoxicity of C17-sphinganine analog mycotoxin (C17-SAMT) using in vitro assays. C17-SAMT was previously identified as the cause of unusual toxicity in cultured mussels from the Bizerte Lagoon in northern Tunisia. While a previous in vivo genotoxicity study was inconclusive, in vitro results demonstrated that C17-SAMT induced an increase in micronucleus formation in human lymphoblastoid TK6 cells at concentrations of 0.87 µM and 1.74 µM. In addition, multiparametric cytotoxicity assays were performed in the human hepatoma HepaRG cell line, which showed that C17-SAMT induced mitochondrial dysfunction, decreased cellular ATP levels, and altered the expression of various proteins, including superoxide dismutase SOD2, heme oxygenase HO-1, and NF-κB. These results suggest that C17-SAMT is mutagenic in vitro and can induce mitochondrial dysfunction in HepaRG cells. However, the exact mode of action of this toxin requires further investigation. Overall, this study highlights the potential toxicity of C17-SAMT and the need for further research to better understand its effects.

Chronic effects of two rutile TiO2 nanomaterials in human intestinal and hepatic cell lines

Background

TiO₂ nanomaterials (NMs) are present in a variety of food and personal hygiene products, and consumers are exposed daily to these NMs through oral exposition. While the bulk of ingested TiO₂ NMs are eliminated rapidly in stool, a fraction is able to cross the intestinal epithelial barrier and enter systemic circulation from where NMs can be distributed to tissues, primarily liver and spleen. Daily exposure to TiO₂ NMs, in combination with a slow rate of elimination from tissues, results in their accumulation within different tissues. Considerable evidence suggests that following oral exposure to TiO₂ NMs, the presence of NMs in tissues is associated with a number of adverse effects, both in intestine and liver. Although numerous studies have been performed in vitro investigating the acute effects of TiO₂ NMs in intestinal and hepatic cell models, considerably less is known about the effect of repeated exposure on these models. In this study, we investigated the cytotoxic effects of repeated exposure of relevant models of intestine and liver to two TiO₂ NMs differing in hydrophobicity for 24 h, 1 week and 2 weeks at concentrations ranging from 0.3 to 80 µg/cm². To study the persistence of these two NMs in cells, we included a 1-week recovery period following 24 h and 1-week treatments. Cellular uptake by TEM and ToF–SIMS analyses, as well as the viability and pro-inflammatory response were evaluated. Changes in the membrane composition in Caco-2 and HepaRG cells treated with TiO₂ NMs for up to 2 weeks were also studied.

Results

Despite the uptake of NM-103 and NM-104 in cells, no significant cytotoxic effects were observed in either Caco-2 or HepaRG cells treated for up to 2 weeks at NM concentrations up to 80 µg/cm²_. In addition, no significant effects on IL-8 secretion were observed. However, significant changes in membrane composition were observed in both cell lines. Interestingly, while most of these phospholipid modifications were reversed following a 1-week recovery, others were not affected by the recovery period.

Conclusion

These findings indicate that although no clear effects on cytotoxicity were observed following repeated exposure of differentiated Caco-2 and HepaRG cells to TiO₂ NMs, subtle effects on membrane composition could induce potential adverse effects in the long-term.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00470-1.

Genotoxic impact of aluminum-containing nanomaterials in human intestinal and hepatic cells

Exposure of consumers to aluminum-containing nanomaterials (Al NMs) is an area of concern for public health agencies. As the available data on the genotoxicity of Al₂O₃ and Al⁰ NMs are inconclusive or rare, the present study investigated their in vitro genotoxic potential in intestinal and liver cell models, and compared with the ionic form AlCl₃. Intestinal Caco-2 and hepatic HepaRG cells were exposed to Al⁰ and Al₂O₃ NMs (0.03 to 80 μg/cm²). Cytotoxicity, oxidative stress and apoptosis were measured using High Content Analysis. Genotoxicity was investigated through γH2AX labelling, the alkaline comet and micronucleus assays. Moreover, oxidative DNA damage and carcinogenic properties were assessed using the Fpg-modified comet assay and the cell transforming assay in Bhas 42 cells respectively. The three forms of Al did not induce chromosomal damage. However, although no production of oxidative stress was detected, Al₂O₃ NMs induced oxidative DNA damage in Caco-2 cells but not likely related to ion release in the cell media. Considerable DNA damage was observed with Al⁰ NMs in both cell lines in the comet assay, likely due to interference with these NMs. No genotoxic effects were observed with AlCl₃. None of the Al compounds induced cytotoxicity, apoptosis, γH2AX or cell transformation.

Genotoxicity of Aluminum and Aluminum Oxide Nanomaterials in Rats Following Oral Exposure

Due to several gaps remaining in the toxicological evaluation of nanomaterials (NMs), consumers and public health agencies have shown increasing concern for human health protection. In addition to aluminum (Al) microparticles, Al-containing nanomaterials (Al NMs) have been applied by food industry as additives and contact materials. Due to the limited amount of literature on the toxicity of Al NMs, this study aimed to evaluate the in vivo genotoxic potential of Al0 and Al2O3 NMs after acute oral exposure. Male Sprague-Dawley rats were administered three successive gavages at 6, 12.5 and 25 mg/kg bw. A comparison with AlCl3 was done in order to assess the potential effect of dissolution into Al ions. Both DNA strand breaks and oxidative DNA damage were investigated in six organs/tissues (duodenum, liver, kidney, spleen, blood and bone marrow) with the alkaline and the Fpg-modified comet assays. Concomitantly, chromosomal damage was investigated in bone marrow and colon with the micronucleus assay. The comet assay only showed DNA damage with Al2O3 NMs in bone marrow (BM), while AlCl3 induced slight but non-significant oxidative DNA damage in blood. No increase of chromosomal mutations was observed after treatment with the two Al MNs either in the BM or in the colons of rats.

Aluminum in liver cells - the element species matters

Aluminum (Al) can be ingested from food and released from packaging and can reach key organs involved in human metabolism, including the liver via systemic distribution. Recent studies discuss the occurrence of chemically distinct Al-species and their interconversion by contact with biological fluids. These Al species can vary with regard to their intestinal uptake, systemic transport, and therefore could have species-specific effects on different organs and tissues. This work aims to assess the in vitro hepatotoxic hazard potential of three different relevant Al species: soluble AlCl₃ and two nanoparticulate Al species were applied, representing for the first time an investigation of metallic nanoparticles besides to mineral bound γ-Al₂O₃ on hepatic cell lines. To investigate the uptake and toxicological properties of the Al species, we used two different human hepatic cell lines: HepG2 and differentiated HepaRG cells. Cellular uptake was determined by different methods including light microscopy, transmission electron microscopy, side-scatter analysis, and elemental analysis. Oxidative stress, mitochondrial dysfunction, cell death mechanisms, and DNA damage were monitored as cellular parameters. While cellular uptake into hepatic cell lines occurred predominantly in the particle form, only ionic AlCl₃ caused cellular effects. Since it is known, that Al species can convert one into another, and mechanisms including 'trojan-horse'-like uptake can lead to an Al accumulation in the cells. This could result in the slow release of Al ions, for which reason further hazard cannot be excluded. Therefore, individual investigation of the different Al species is necessary to assess the toxicological potential of Al particles.

Uptake and molecular impact of aluminum-containing nanomaterials on human intestinal caco-2 cells

Aluminum (Al) is one of the most common elements in the earth crust and increasingly used in food, consumer products and packaging. Its hazard potential for humans is still not completely understood. Besides the metallic form, Al also exists as mineral, including the insoluble oxide, and in soluble ionic forms. Representatives of these three species, namely a metallic and an oxidic species of Al-containing nanoparticles and soluble aluminum chloride, were applied to human intestinal cell lines as models for the intestinal barrier. We characterized physicochemical particle parameters, protein corona composition, ion release and cellular uptake. Different in vitro assays were performed to determine potential effects and molecular modes of action related to the individual chemical species. For a deeper insight into signaling processes, microarray transcriptome analyses followed by bioinformatic data analysis were employed. The particulate Al species showed different solubility in biological media. Metallic Al nanoparticles released more ions than Al₂O₃ nanoparticles, while AlCl₃ showed a mixture of dissolved and agglomerated particulate entities in biological media. The protein corona composition differed between both nanoparticle species. Cellular uptake, investigated in transwell experiments, occurred predominantly in particulate form, whereas ionic Al was not taken up by intestinal cell lines. Transcellular transport was not observed. None of the Al species showed cytotoxic effects up to 200 µg Al/mL. The transcriptome analysis indicated mainly effects on oxidative stress pathways, xenobiotic metabolism and metal homeostasis. We have shown for the first time that intestinal cellular uptake of Al occurs preferably in the particle form, while toxicological effects appear to be ion-related.

Genotoxic effects of food contact recycled paperboard extracts on two human hepatic cell lines

Food contact paperboards may be a potential source of food contamination as they can release chemicals (intentionally added or not), especially recycled paperboards. This study assessed the in vitro genotoxicity of food contact paperboard samples from a manufacturer, collected at the beginning and at the end of a recycling production chain. Samples were extracted in water to mimic a wet food contact. Different genotoxic endpoints were evaluated in two human hepatic cell lines (HepG2 and HepaRG) using bioassays: γH2AX and p53 activation, primary DNA damage with the comet assay and micronucleus formation. It was found that the samples from the beginning and the end of the production chain induced, with the same potency, γH2AX and p53-ser15 activation and DNA damage with the comet assay. The micronucleus assay was negative with the paperboard extract from the beginning of the chain, whereas positive data were observed for the end paperboard extract. These results indicate that samples from recycled food contact paperboard can induce in vitro genotoxic effects in this study's experimental conditions.

Toxicity, genotoxicity and proinflammatory effects of amorphous nanosilica in the human intestinal Caco-2 cell line

Silica (SiO2) in its nanosized form is now used in food applications although the potential risks for human health need to be evaluated in further detail. In the current study, the uptake of 15 and 55nm colloidal SiO2 NPs in the human intestinal Caco-2 cell line was investigated by transmission electron microscopy. The ability of these NPs to induce cytotoxicity (XTT viability test), genotoxicity (γH2Ax and micronucleus assay), apoptosis (caspase 3), oxidative stress (oxidation of 2,7-dichlorodihydrofluorescein diacetate probe) and proinflammatory effects (interleukin IL-8 secretion) was evaluated. Quartz DQ12 was used as particle control. XTT and cytokinesis-block micronucleus assays revealed size- and concentration-dependent effects on cell death and chromosome damage following exposure to SiO2 nanoparticles, concomitantly with generation of reactive oxygen species (ROS), SiO2-15nm particles being the most potent. In the same way, an increased IL-8 secretion was only observed with SiO2-15nm at the highest tested dose (32μg/ml). TEM images showed that both NPs were localized within the cytoplasm but did not enter the nucleus. SiO2-15nm, and to a lower extent SiO2-55nm, exerted toxic effects in Caco-2 cells. The observed genotoxic effects of these NPs are likely to be mediated through oxidative stress rather than a direct interaction with the DNA. Altogether, our results indicate that exposure to SiO2 NPs may induce potential adverse effects on the intestinal epithelium in vivo.

Cytotoxicity, fractionation and dereplication of extracts of the dinoflagellate Vulcanodinium rugosum, a producer of pinnatoxin G

Pinnatoxin G (PnTX-G) is a marine toxin belonging to the class of cyclic imines and produced by the dinoflagellate Vulcanodinium rugosum. In spite of its strong toxicity to mice, leading to the classification of pinnatoxins into the class of “fast-acting toxins”, its hazard for human health has never been demonstrated. In this study, crude extracts of V. rugosum exhibited significant cytotoxicity against Neuro2A and KB cells. IC₅₀ values of 0.38 µg mL⁻¹ and 0.19 µg mL⁻¹ were estimated on Neuro2A cells after only 24 h of incubation and on KB cells after 72 h of incubation, respectively. In the case of Caco-2 cells 48 h after exposure, the crude extract of V. rugosum induced cell cycle arrest accompanied by a dramatic increase in double strand DNA breaks, although only 40% cytotoxicity was observed at the highest concentration tested (5 µg mL⁻¹). However, PnTX-G was not a potent cytotoxic compound as no reduction of the cell viability was observed on the different cell lines. Moreover, no effects on the cell cycle or DNA damage were observed following treatment of undifferentiated Caco-2 cells with PnTX-G. The crude extract of V. rugosum was thus partially purified using liquid-liquid partitioning and SPE clean-up. In vitro assays revealed strong activity of some fractions containing no PnTX-G. The crude extract and the most potent fraction were evaluated using full scan and tandem high resolution mass spectrometry. The dereplication revealed the presence of a major compound that could be putatively annotated as nakijiquinone A, N-carboxy-methyl-smenospongine or stachybotrin A, using the MarinLit™ database. Further investigations will be necessary to confirm the identity of the compounds responsible for the cytotoxicity and genotoxicity of the extracts of V. rugosum.

Specific pesticide-dependent increases in α-synuclein levels in human neuroblastoma (SH-SY5Y) and melanoma (SK-MEL-2) cell lines

Epidemiological studies indicate a role of genetic and environmental factors in Parkinson's disease involving alterations of the neuronal α-synuclein (α-syn) protein. In particular, a relationship between Parkinson's disease and occupational exposure to pesticides has been repeatedly suggested. Our objective was to precisely assess changes in α-syn levels in human neuroblastoma (SH-SY5Y) and melanoma (SK-MEL-2) cell lines following acute exposure to pesticides (rotenone, paraquat, maneb, and glyphosate) using Western blot and flow cytometry. These human cell lines express α-syn endogenously, and overexpression of α-syn (wild type or mutated A53T) can be obtained following recombinant adenoviral transduction. We found that endogenous α-syn levels in the SH-SY5Y neuroblastoma cell line were markedly increased by paraquat, and to a lesser extent by rotenone and maneb, but not by glyphosate. Rotenone also clearly increased endogenous α-syn levels in the SK-MEL-2 melanoma cell line. In the SH-SY5Y cell line, similar differences were observed in the α-syn adenovirus-transduced cells, with a higher increase of the A53T mutated protein. Paraquat markedly increased α-syn in the SK-MEL-2 adenovirus-transduced cell line, similarly for the wild-type or A53T proteins. The observed differences in the propensities of pesticides to increase α-syn levels are in agreement with numerous reports that indicate a potential role of exposure to certain pesticides in the development of Parkinson's disease. Our data support the hypothesis that pesticides can trigger some molecular events involved in this disease and also in malignant melanoma that consistently shows a significant but still unexplained association with Parkinson's disease.

Comparative cytotoxicity, oxidative stress, and cytokine secretion induced by two cyanotoxin variants, microcystin LR and RR, in human intestinal Caco-2 cells

While MC-LR and MC-RR share significant structural similarity, MC-RR is less cytotoxic than MC-LR. In the current study, we have compared the effects of MC-LR and MC-RR in Caco-2 cells by evaluating cytotoxicity, oxidative stress (reactive oxygen species production), and the cellular proinflammatory response (IL-6 and IL-8 production). Following treatment with 100 µM microcystins (MC), cytotoxicity was two-fold greater with MC-LR as compared to MC-RR after 24 h exposure. Whereas the reactive oxygen species production and IL-6 secretion were similar following a 24-h treatment with either MC, 100 µM MC-LR induced a five-fold greater IL-8 secretion when compared to MC-RR. Our study has demonstrated that, although both MC-LR and MC-RR induced some cytotoxicity in human intestinal cells, a major difference in IL-8 production was observed between the two variants.

Sex hormone-binding globulin gene expression in the liver: drugs and the metabolic syndrome

Sex hormone-binding globulin (SHBG) is the main transport binding protein for sex steroid hormones in plasma and regulates their accessibility to target cells. Plasma SHBG is secreted by the liver under the control of hormones and nutritional factors. In the human hepatoma cell line (HepG2), thyroid and estrogenic hormones, and a variety of drugs including the antioestrogen tamoxifen, the phytoestrogen, genistein and mitotane (Op'DDD) increase SHBG production and SHBG gene promoter activity. In contrast, monosaccharides (glucose or fructose) effectively decrease SHBG expression by inducing lipogenesis, which reduces hepatic HNF-4alpha levels, a transcription factor that play a critical role in controlling the SHBG promoter. Interestingly, diminishing hepatic lipogenesis and free fatty acid liver biosynthesis also appear to be associated with the positive effects of thyroid hormones and PPARgamma antagonists on SHBG expression. This mechanism provides a biological explanation for why SHBG is a sensitive biomarker of insulin resistance and the metabolic syndrome, and why low plasma SHBG levels are a risk factor for developing hyperglycemia and type 2 diabetes, especially in women. These important advances in our knowledge of the regulation of SHBG expression in the liver open new approaches for identifying and preventing metabolic disorder-associated diseases early in life.

Specialized rules of gene transcription in male germ cells: the CREM paradigm

Specialized transcription complexes that coordinate the differentiation programme of spermatogenesis have been found in germ cells, which display specific differences in the components of the general transcription machinery. The TATA-binding protein family and its associated cofactors, for example, show upregulated expression in testis. In this physiological context, transcriptional control mediated by the activator cAMP response element modulator (CREM) represents an established paradigm. Somatic cell activation by CREM requires its phosphorylation at a unique regulatory site (Ser117) and subsequent interaction with the ubiquitous coactivator CREB-binding protein. In testis, CREM transcriptional activity is controlled through interaction with a tissue-specific partner, activator of CREM in the testis (ACT), which confers a powerful, phosphorylation-independent activation capacity. The function of ACT was found to be regulated by the testis-specific kinesin KIF17b. Here we discuss some aspects of the testis-specific transcription machinery, whose function is essential for the process of spermatogenesis.

A specific programme of gene transcription in male germ cells

The differentiation of male germ cell requires spermatogenic stage and cell-specific gene expression that is achieved by unique chromatin remodelling, transcriptional control, and the expression of testis-specific genes or isoforms. Specialized transcription complexes that coordinate the differentiation programme of spermatogenesis have been found in germ cells, which display specific differences in the components of the general transcription machinery. The TATA-binding (TBP) protein family and its associated co-factors, for example, show upregulated expression in testis. In this physiological context, transcriptional control mediated by the activator CREM represents an established paradigm. In somatic cells, activation by CREM requires its phosphorylation at a unique regulatory site (Ser117) and subsequent interaction with the ubiquitous coactivator CBP. In testis, CREM transcriptional activity is controlled through interaction with a tissue-specific partner, ACT, which confers a powerful, phosphorylation-independent activation capacity. The function of ACT is regulated by a testis-specific kinesin, KIF17b. This study discusses some aspects of the testis-specific transcription machinery, the function of which is essential for the process of spermatogenesis.