Genotoxicity of Graphene-Based Materials

In vitro evaluation of the toxicity mechanisms of two functionalized reduced graphene oxide derivatives

Dodecyl amine functionalized reduced graphene oxide (DA-rGO) and [2-(methacryloyloxy) ethyl] trimethylammonium chloride functionalized rGO (MTAC-rGO) have been developed and characterised for their further use in the food packaging industry as food contact materials. But before their application, an authorization procedure is required in which their safety plays a key role. Therefore, the aim of this work was to evaluate their toxicity with focus on two different toxicity mechanisms: genotoxicity and immunotoxicity. Following the recommendations of the European Food Safety Authority, the mutagenicity and genotoxicity were evaluated by the mouse lymphoma assay and the micronucleus assay, respectively, in L5178Y TK cells. Both assays did not show any effect at the tested concentrations (up to 200 μg/mL). The potential immunotoxicity was evaluated on two human cell lines: THP-1 (monocytes) and Jurkat (lymphocytes). The results showed that the highest cytotoxicity was induced by MTAC-rGO in Jurkat cells. The two functionalized rGO compounds did not significantly affect the differentiation process of monocytes into macrophages. In general, both compounds altered the expression of different cytokines, with the most prominent changes observed with MTAC-rGO in THP-1 cells. Moreover, MTAC-rGO induced the most evident differences in markers of cell death mechanisms. Also, for this graphene derivative, increased levels of IL-1β and TNF-α in THP-1 cell supernatants were observed by ELISA. In conclusion, a case-by-case evaluation is necessary as both functionalized rGO compounds exhibit distinct toxicity profiles that warrant further investigation before their application in the food industry.

Elucidation of Potential Genotoxicity of MXenes Using a DNA Comet Assay

MXenes are among the most diverse and prominent 2D materials. They are being explored in almost every field of science and technology, including biomedicine. In particular, they are being investigated for photothermal therapy, drug delivery, medical imaging, biosensing, tissue engineering, blood dialysis, and antibacterial coatings. Despite their proven biocompatibility and low cytotoxicity, their genotoxicity has not been addressed. To investigate whether MXenes interfere with DNA integrity in cultured cells, we loaded the cells with MXenes and examined the fragmentation of their chromosomal DNA by a DNA comet assay. The presence of both Ti3C2Tx and Nb4C3Tx MXenes generated DNA comets, suggesting a strong genotoxic effect in murine melanoma and human fibroblast cells. However, no corresponding cytotoxicity was observed, confirming that MXenes were well tolerated by the cells. The lateral size of the MXene flakes was critical for developing the DNA comets; submicrometer flakes induced the DNA comets, while larger flakes did not. MXenes did not induce DNA comets in dead cells. Moreover, the extraction of the chromosomal DNA from the MXene-loaded cells or mixing the purified DNA with MXenes showed no signs of DNA fragmentation. Unconstrained living MXene-loaded cells did not show cleavage of the DNA with MXenes under electrophoresis conditions. Thus, the DNA comet assay showed the ability of submicrometer MXene particles to penetrate living cells and induce DNA fragmentation under the applied field. The most probable mechanism of DNA comet formation is the rotation and movement of submicrometer MXene flakes inside cells in an electric field, leading to cleavage and DNA shredding by MXene's razor-sharp edges. Under all other conditions of interest, titanium- and niobium-carbide-based MXenes showed excellent biocompatibility and no signs of cytotoxicity or genotoxicity. These findings may contribute to the development of strategies for cancer therapy.

MicroRNA-Dependent Mechanisms Underlying the Function of a β-Amino Carbonyl Compound in Glioblastoma Cells

Glioblastoma (GB) is an aggressive brain malignancy characterized by its invasive nature. Current treatment has limited effectiveness, resulting in poor patients' prognoses. β-Amino carbonyl (β-AC) compounds have gained attention due to their potential anticancerous properties. In vitro assays were performed to evaluate the effects of an in-house synthesized β-AC compound, named SHG-8, upon GB cells. Small RNA sequencing (sRNA-seq) and biocomputational analyses investigated the effects of SHG-8 upon the miRNome and its bioavailability within the human body. SHG-8 exhibited significant cytotoxicity and inhibition of cell migration and proliferation in U87MG and U251MG GB cells. GB cells treated with the compound released significant amounts of reactive oxygen species (ROS). Annexin V and acridine orange/ethidium bromide staining also demonstrated that the compound led to apoptosis. sRNA-seq revealed a shift in microRNA (miRNA) expression profiles upon SHG-8 treatment and significant upregulation of miR-3648 and downregulation of miR-7973. Real-time polymerase chain reaction (RT-qPCR) demonstrated a significant downregulation of CORO1C, an oncogene and a player in the Wnt/β-catenin pathway. In silico analysis indicated SHG-8's potential to cross the blood-brain barrier. We concluded that SHG-8's inhibitory effects on GB cells may involve the deregulation of various miRNAs and the inhibition of CORO1C.

Biological Effects of Small Sized Graphene Oxide Nanosheets on Human Leukocytes

Since the discovery of graphene, there has been a wide range of the literature dealing with its versatile structure and easy binding of biomolecules as well as its large loading capacity. In the emerging field of immunotherapy, graphene and its derivatives have potential uses as drug delivery platforms directly into tumour sites or as adjuvants in cancer vaccines, as they are internalized by monocytes which in turn may activate adaptive anti-tumoral immune responses. In this study, we expose cells of the innate immune system and a human acute monocytic leukemia cell line (THP-1) to low doses of small-sized GO nanosheets functionalized with bovine serum albumin (BSA) and fluorescein isothiocyanate (FITC), to study their acute response after internalization. We show by flow cytometry, uptake in cells of GO-BSA-FITC reaches 80% and cell viability and ROS production are both unaffected by exposure to nanoparticles. On the contrary, GO-BSA nanosheets seem to have an inhibitory effect on ROS production, probably due to their antioxidant properties. We also provided results on chemotaxis of macrophages derived from peripheral blood monocytes treated with GO-BSA. In conclusion, we showed the size of nanosheets, the concentration used and the degree of functionalization were important factors for biocompatibility of GO in immune cells. Its low cytotoxicity and high adaptability to the cells of the innate immune system make it a good candidate for deployment in immunotherapy, in particular for delivering protein antigens to monocytes which activate adaptive immunity.

Graphene-Based Engineered Living Materials

With the rise of engineered living materials (ELMs) as innovative, sustainable and smart systems for diverse engineering and biological applications, global interest in advancing ELMs is on the rise. Graphene-based nanostructures can serve as effective tools to fabricate ELMs. By using graphene-based materials as building units and microorganisms as the designers of the end materials, next-generation ELMs can be engineered with the structural properties of graphene-based materials and the inherent properties of the microorganisms. However, some challenges need to be addressed to fully take advantage of graphene-based nanostructures for the design of next-generation ELMs. This work covers the latest advances in the fabrication and application of graphene-based ELMs. Fabrication strategies of graphene-based ELMs are first categorized, followed by a systematic investigation of the advantages and disadvantages within each category. Next, the potential applications of graphene-based ELMs are covered. Moreover, the challenges associated with fabrication of next-generation graphene-based ELMs are identified and discussed. Based on a comprehensive overview of the literature, the primary challenge limiting the integration of graphene-based nanostructures in ELMs is nanotoxicity arising from synthetic and structural parameters. Finally, we present possible design principles to potentially address these challenges.

Role of Chemical Reduction and Formulation of Graphene Oxide on Its Cytotoxicity towards Human Epithelial Bronchial Cells

Graphene-based materials may pose a potential risk for human health due to occupational exposure, mainly by inhalation. This study was carried out on bronchial epithelial 16HBE14o- cells to evaluate the role of chemical reduction and formulation of graphene oxide (GO) on its cytotoxic potential. To this end, the effects of GO were compared to its chemically reduced form (rGO) and its stable water dispersion (wdGO), by means of cell viability reduction, reactive oxygen species (ROS) generation, pro-inflammatory mediators release and genotoxicity. These materials induced a concentration-dependent cell viability reduction with the following potency rank: rGO > GO >> wdGO. After 24 h exposure, rGO reduced cell viability with an EC50 of 4.8 μg/mL (eight-fold lower than that of GO) and was the most potent material in inducing ROS generation, in contrast to wdGO. Cytokines release and genotoxicity (DNA damage and micronucleus induction) appeared low for all the materials, with wdGO showing the lowest effect, especially for the former. These results suggest a key role for GO reduction in increasing GO cytotoxic potential, probably due to material structure alterations resulting from the reduction process. In contrast, GO formulated in a stable dispersion seems to be the lowest cytotoxic material, presumably due to its lower cellular internalization and damaging capacity.

Impact of physico-chemical properties on the toxicological potential of reduced graphene oxide in human bronchial epithelial cells

The increasing use of graphene-based materials (GBM) requires their safety evaluation, especially in occupational settings. The same physico-chemical (PC) properties that confer GBM extraordinary functionalities may affect the potential toxic response. Most toxicity assessments mainly focus on graphene oxide and rarely investigate GBMs varying only by one property. As a novelty, the present study assessed the in vitro cytotoxicity and genotoxicity of six reduced graphene oxides (rGOs) with different PC properties in the human bronchial epithelial 16HBE14o - cell line. Of the six materials, rGO1-rGO4 only differed in the carbon-to-oxygen (C/O) content, whereas rGO5 and rGO6 were characterized by different lateral size and number of layers, respectively, but similar C/O content compared with rGO1. The materials were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, laser diffraction and dynamic light scattering, and Brunauer-Emmett-Teller analysis. Cytotoxicity (Luminescent Cell Viability and WST-8 assays), the induction of reactive oxygen species (ROS; 2',7'-dichlorofluorescin diacetate-based assay), the production of cytokines (enzyme-linked immunosorbent assays) and genotoxicity (comet and micronucleus assays) were evaluated. Furthermore, the internalization of the materials in the cells was confirmed by laser confocal microscopy. No relationships were found between the C/O ratio or the lateral size and any of the rGO-induced biological effects. However, rGO of higher oxygen content showed higher cytotoxic and early ROS-inducing potential, whereas genotoxic effects were observed with the rGO of the lowest density of oxygen groups. On the other hand, a higher number of layers seems to be associated with a decreased potential for inducing cytotoxicity and ROS production.

Age- and Lifespan-Dependent Differences in GO Caused DNA Damage in Acheta domesticus

The rising applicability of graphene oxide (GO) should be preceded by detailed tests confirming its safety and lack of toxicity. Sensitivity to GO of immature, or with different survival strategy, individuals has not been studied so far. Therefore, in the present research, we focused on the GO genotoxic effects, examining selected parameters of DNA damage (total DNA damage, double-strand breaks-DSB, 8-hydroxy-2'-deoxyguanosine-8-OHdG, abasic site-AP sites), DNA damage response parameters, and global methylation in the model organism Acheta domesticus. Special attention was paid to various life stages and lifespans, using wild (H), and selected for longevity (D) strains. DNA damage was significantly affected by stage and/or strain and GO exposure. Larvae and young imago were generally more sensitive than adults, revealing more severe DNA damage. Especially in the earlier life stages, the D strain reacted more intensely/inversely than the H strain. In contrast, DNA damage response parameters were not significantly related to stage and/or strain and GO exposure. Stage-dependent DNA damage, especially DSB and 8-OHdG, with the simultaneous lack or subtle activation of DNA damage response parameters, may result from the general life strategy of insects. Predominantly fast-living and fast-breeding organisms can minimize energy-demanding repair mechanisms.