A novel approach to increase robustness, precision and high-throughput capacity of single cell gel electrophoresis

Assessing Genotoxicity of Ten Different Engineered Nanomaterials by the Novel Semi-Automated FADU Assay and the Alkaline Comet Assay

Increased engineered nanomaterial (ENM) production and incorporation in consumer and biomedical products has raised concerns about the potential adverse effects. The DNA damaging capacity is of particular importance since damaged genetic material can lead to carcinogenesis. Consequently, reliable and robust in vitro studies assessing ENM genotoxicity are of great value. We utilized two complementary assays based on different measurement principles: (1) comet assay and (2) FADU (fluorimetric detection of alkaline DNA unwinding) assay. Assessing cell viability ruled out false-positive results due to DNA fragmentation during cell death. Potential structure–activity relationships of 10 ENMs were investigated: three silica nanoparticles (SiO₂-NP) with varying degrees of porosity, titanium dioxide (TiO₂-NP), polystyrene (PS-NP), zinc oxide (ZnO-NP), gold (Au-NP), graphene oxide (GO) and two multi-walled carbon nanotubes (MWNT). SiO₂-NPs, TiO₂-NP and GO were neither cytotoxic nor genotoxic to Jurkat E6-I cells. Quantitative interference corrections derived from GO results can make the FADU assay a promising screening tool for a variety of ENMs. MWNT merely induced cytotoxicity, while dose- and time-dependent cytotoxicity of PS-NP was accompanied by DNA fragmentation. Hence, PS-NP served to benchmark threshold levels of cytotoxicity at which DNA fragmentation was expected. Considering all controls revealed the true genotoxicity for Au-NP and ZnO-NP at early time points.

B-Comet Assay (Comet Assay on Buccal Cells) for the Evaluation of Primary DNA Damage in Human Biomonitoring Studies

Many subjects perceive venous blood collection as too invasive, and thus moving to better-accepted procedures for leukocytes collection might be crucial in human biomonitoring studies (e.g., biomonitoring of occupational or residential exposure to genotoxins) management. In this context, primary DNA damage was assessed in buccal lymphocytes (BLs), fresh whole venous, and capillary blood leukocytes, and compared with that in peripheral blood lymphocytes (PBLs)—the most frequently used cells—in 15 young subjects. Mouthwashes were collected after the volunteers rinsed their mouths with normal saline, and BLs were isolated by density gradient centrifugation. Blood samples were collected by venipuncture or by lancet. Anthropometric and lifestyle information was obtained by the administration of a structured questionnaire. As shown in the Bland-Altman plots, the level of agreement between BLs and PBLs lied within the accepted range, we thus enrolled a wider population (n = 54) to assess baseline DNA damage in BLs. In these cells, mean values of tail length (µm), tail intensity (%), and tail moment were 25.7 ± 0.9, 6.7 ± 0.4 and 1.0 ± 0.1, respectively. No significant association was observed between sex and smoking habit with any of the DNA damage parameters. Conversely, underweight subjects displayed significantly higher genomic instability compared with normal weight group (p < 0.05). In conclusion, we successfully managed to set up and update a non-invasive and well-accepted procedure for the isolation of BLs from saliva that could be useful in upcoming biomonitoring studies.

Exploring Flow Cytometry-Based Micronucleus Scoring for Reliable Nanomaterial Genotoxicity Assessment

The increased use of engineered nanomaterials (ENM) such as SiO₂ and TiO₂ in industrial products, especially in food, raises concerns with regard to their effect on human health. In particular, ENM-induced genotoxicity is crucial to investigate, since DNA damage can cause induction or promotion of carcinogenesis. However, current in vitro and in vivo nanogenotoxicological data are highly contradictory, which impedes interpretation and extrapolation. Hence, robust, reliable, and ideally scalable in vitro methods for nanogenotoxicity assessment are of great interest. This work aimed at evaluating the suitability of flow cytometry-based micronuclei scoring for reliable nanogenotoxicological assessment in human intestinal cells. Therefore, we have evaluated the genotoxicity of differently sized SiO₂ and TiO₂ from different sources (food-relevant, commercially available, and laboratory-synthesized) using the well-established alkaline single cell gel electrophoresis (Comet assay) and the micronucleus (MN) assay employing a flow cytometric readout. Our study demonstrates that physiologically relevant doses of several types of SiO₂ and TiO₂ did not cause genotoxicity, as assessed by the Comet assay, and the MN flow cytometry assay under the particular experimental conditions described. To improve data reliability, we identified ENM-induced interferences with flow cytometric scoring employing a set of interference controls, which is generally applicable for any nanomaterial and any cell line. In conclusion, flow cytometry-based MN scoring appears to be a promising methodology in nanogenotoxicity testing since data acquisition and analysis are significantly faster, highly scalable in terms of throughput, and less operator-dependent compared to the traditional microscopic evaluation. In particular, ENM-induced false-positive or false-negative results, which have not been addressed sufficiently in the literature, can be detected easily, thus enhancing data reliability.

Applications of CometChip for Environmental Health Studies

Environmental exposures have long been known to impact public health and safety. For example, exposures to airborne particulates, heavy metals in water, or certain industrial chemicals can contribute to aging and to risk of developing cancer and other diseases. Environmental factors can impact health in a variety of ways, but a key concern is DNA damage, which can lead to mutations that cause cancer. Cancer can take years to develop following chemical exposure; however, one way to predict carcinogenicity in a more practical time frame is by studying the chemical's ability to induce DNA damage. The comet assay (or single-cell gel electrophoresis assay) has been used successfully for genotoxicity testing. The comet assay allows for the detection of DNA strand breaks via analysis of DNA migration during electrophoresis. Previously, the Engelward laboratory, in collaboration with the Bhatia laboratory, developed the CometChip for measurements of DNA damage and repair. The CometChip is a high-throughput comet assay that improves user reproducibility and significantly shortens total assay time. Here, we describe how the high-throughput CometChip platform can be used to measure DNA damage in established cell lines, animal models, and human samples. We also discuss technical challenges associated with these studies and provide recommendations on how to achieve optimal results for researchers interested in adopting this assay.

Innovative Techniques and Strategies for a Reliable High-Throughput Genotoxicity Assessment

Damage to DNA is a central mechanism to the initiation of carcinogenesis. As a consequence, precise DNA damage detection is essential for an effective risk assessment of xenobiotics and constitutes a powerful tool for human biomonitoring and early stage cancer risk assessment. Here we highlight four innovative approaches for determining genotoxicity in a reliable and in the future high-throughput manner. In this context, we discuss and evaluate recent improvements to well-established methods and present promising new techniques.