Uptake of label-free graphene oxide by Caco-2 cells is dependent on the cell differentiation status

Boron Nitride Nanosheets Induce Lipid Accumulation and Autophagy in Human Alveolar Lung Epithelial Cells Cultivated at Air-Liquid Interface

Hexagonal boron nitride (hBN) is an emerging 2D material attracting significant attention due to its superior electrical, chemical, and therapeutic properties. However, inhalation toxicity mechanisms of hBN in human lung cells are poorly understood. Here, cellular interaction and effects of hBN nanosheets is investigated in alveolar epithelial cells cultured on porous inserts and exposed under air-liquid interface conditions for 24 h. hBN is taken up by the cells as determined in a label-free manner via RAMAN-confocal microscopy, ICP-MS, TEM, and SEM-EDX. No significant (p > 0.05) effects are observed on cell membrane integrity (LDH release), epithelial barrier integrity (TEER), interleukin-8 cytokine production or reactive oxygen production at tested dose ranges (1, 5, and 10 µg cm-2). However, it is observed that an enhanced accumulation of lipid granules in cells indicating the effect of hBN on lipid metabolism. In addition, it is observed that a significant (p < 0.05) and dose-dependent (5 and 10 µg cm-2) induction of autophagy in cells after exposure to hBN, potentially associated with the downstream processing and breakdown of excess lipid granules to maintain lipid homeostasis. Indeed, lysosomal co-localization of lipid granules supporting this argument is observed. Overall, the results suggest that the continuous presence of excess intracellular lipids may provoke adverse outcomes in the lungs.

Environmental and Health Impacts of Graphene and Other Two-Dimensional Materials: A Graphene Flagship Perspective

Two-dimensional (2D) materials have attracted tremendous interest ever since the isolation of atomically thin sheets of graphene in 2004 due to the specific and versatile properties of these materials. However, the increasing production and use of 2D materials necessitate a thorough evaluation of the potential impact on human health and the environment. Furthermore, harmonized test protocols are needed with which to assess the safety of 2D materials. The Graphene Flagship project (2013-2023), funded by the European Commission, addressed the identification of the possible hazard of graphene-based materials as well as emerging 2D materials including transition metal dichalcogenides, hexagonal boron nitride, and others. Additionally, so-called green chemistry approaches were explored to achieve the goal of a safe and sustainable production and use of this fascinating family of nanomaterials. The present review provides a compact survey of the findings and the lessons learned in the Graphene Flagship.

Few-layered graphene increases the response of nociceptive neurons to irritant stimuli

The unique properties of few-layered graphene (FLG) make it interesting for a variety of applications, including biomedical applications, such as tissue engineering and drug delivery. Although different studies focus on applications in the central nervous system, its interaction with the peripheral nervous system has been so far overlooked. Here, we investigated the effects of exposure to colloidal dispersions of FLG on the sensory neurons of the rat dorsal root ganglia (DRG). We found that the FLG flakes were actively internalized by sensory neurons, accumulated in large intracellular vesicles, and possibly degraded over time, without major toxicological concerns, as neuronal viability, morphology, protein content, and basic electrical properties of DRG neurons were preserved. Interestingly, in our electrophysiological investigation under noxious stimuli, we observed an increased functional response upon FLG treatment of the nociceptive subpopulation of DRG neurons in response to irritants specific for chemoreceptors TRPV1 and TRPA1. The observed effects of FLG on DRG neurons may open-up novel opportunities for applications of these materials in specific disease models.

X-ray radio-enhancement by Ti3C2Tx MXenes in soft tissue sarcoma

Radiotherapy is a cornerstone of cancer treatment. However, due to the low tissue specificity of ionizing radiation, damage to the surrounding healthy tissue of the tumor remains a significant challenge. In recent years, radio-enhancers based on inorganic nanomaterials have gained considerable interest. Beyond the widely explored metal and metal oxide nanoparticles, 2D materials, such as MXenes, could present potential benefits because of their inherently large specific surface area. In this study, we highlight the promising radio-enhancement properties of Ti3C2Tx MXenes. We demonstrate that atomically thin layers of titanium carbides (Ti3C2Tx MXenes) are efficiently internalized and well-tolerated by mammalian cells. Contrary to MXenes suspended in aqueous buffers, which fully oxidize within days, yielding rice-grain shaped rutile nanoparticles, the MXenes internalized by cells oxidize at a slower rate. This is consistent with cell-free experiments that have shown slower oxidation rates in cell media and lysosomal buffers compared to dispersants without antioxidants. Importantly, the MXenes exhibit robust radio-enhancement properties, with dose enhancement factors reaching up to 2.5 in human soft tissue sarcoma cells, while showing no toxicity to healthy human fibroblasts. When compared to oxidized MXenes and commercial titanium dioxide nanoparticles, the intact 2D titanium carbide flakes display superior radio-enhancement properties. In summary, our findings offer evidence for the potent radio-enhancement capabilities of Ti3C2Tx MXenes, marking them as a promising candidate for enhancing radiotherapy.

Cellular and bioenergetic effects of polystyrene microplastic in function of cell type, differentiation status and post-exposure time

The ubiquity of microplastics (MPs) in food sources and personal care products increasingly raises concerns on human health. However, little is known about the duration of the effects of MPs and whether effects depend on cellular differentiation status. Herein, cellular and bioenergetic effects of MPs in different exposure scenarios on four types of human cell lines derived from lung (A549 and BEAS-2B), colon (Caco-2) and liver (HepG2) were investigated. These cell lines are models for the major exposure routes in the body (inhalation, ingestion and physiological transport through the liver by the portal vein). To this aim, different scenarios were implemented by exposing undifferentiated and differentiated cells to single dosing of 2-μm polystyrene (PS) (102-105 particles/mL) for 48 h and 12 days. The undifferentiated Caco-2 cells with short exposure (48 h) showed the highest uptake rate of PS yet without significant cellular and mitochondrial responses. The biological effects, with the exception of ROS production, were not influenced by differentiation states of A549 and Caco-2 cells although differentiated cells showed much weaker ability to internalize PS. However, PS had significantly long-term impacts on cellular and mitochondrial functions even after the initial exposure period. In particular, Caco-2 cells that were post-exposed for 12 days after single PS dosing suffered higher oxidative stress and exhibited mitochondrial dysfunction than that for short exposure. Correspondingly, we observed that PS particles still remained in cell membrane and even in nuclei with high retention rate by 14-d post exposure during which metabolism and exchange of internalization and release occurred in cells. This indicates PS could induce chronic stress and even harmful effects on human cells after single intake that persists for a long time. This study paves the way for assessing the influence of PS on human health at low particle concentrations and with multiple exposure scenarios.

Transglycosylation catalysed by Caco-2 membrane disaccharidases: A new approach to understand carbohydrates digestibility

Under appropriate experimental conditions, some glycoside hydrolases can catalyze transglycosylation reactions; a hypothesis associated with this is that the glycosidic linkages formed will be preferentially hydrolyzed under optimal conditions. Therefore, the hydrolytic and transglycosylation activities of isolated membranes from differentiated Caco-2 cells on sucrose, maltose and isomaltulose were evaluated. After the enzymatic reactions, the di- and trisaccharides obtained were identified by gas chromatography coupled to a mass spectrometer. Differentiated Caco-2 cell membranes exerted hydrolytic and transglycosylation activities towards the studied disaccharides. The obtained di- and trisaccharides were detected for the first time using human cell models. Due to the absence of maltase-glucoamylase complex (MGAM) in Caco-2 cells, and the known hydrolytic activity of sucrase-isomaltase (SI) towards sucrose, maltose and isomaltulose, it is plausible that the glycosidic linkages obtained after the transglycosylation reaction, mainly α-glucosyl-fructoses and α-glucosyl-glucoses, were carried out by SI complex. This approach can be used as a model to explain carbohydrate digestibility in the small intestine and as a tool to design new oligosaccharides with low intestinal digestibility.

Harnessing graphene oxide nanocarriers for siRNA delivery in a 3D spheroid model of lung cancer

Gene therapy has been recently proposed as an effective strategy for cancer treatment. A significant body of literature proved the effectiveness of nanocarriers to deliver therapeutic agents to 2D tumour models, which are simple but not always representative of the in vivo reality. In this study, we analyze the efficiency of 3D spheroids combined with a minimally modified graphene oxide (GO)-based nanocarrier for siRNA delivery as a new system for cell transfection. Small interfering RNA (siRNA) targeting cluster of differentiation 47 (CD47; CD47_siRNA) was used as an anti-tumour therapeutic agent to silence the genes expressing CD47. This is a surface marker able to send a "don't eat me" signal to macrophages to prevent their phagocytosis. Also, we report the analysis of different GO formulations, in terms of size (small: about 100 nm; large: >650 nm) and functionalization (unmodified or modified with polyethylene glycol (PEG) and the dendrimer PAMAM), aiming to establish the efficiency of unmodified GO as a nanocarrier for the transfection of A549 lung cancer spheroids. Small modified GO (smGO) showed the highest transfection efficiency values (>90%) in 3D models. Interestingly, small unmodified GO (sGO) was found to be promising for transfection, with efficiency values >80% using a higher siRNA ratio (i.e., 3 : 1). These results demonstrated the higher efficiency of spheroids compared to 2D models for transfection, and the high potential of unmodified GO to carry siRNA, providing a promising new in vitro model system for the analysis of anticancer gene therapies.

Impact of Gastrointestinal Digestion In Vitro Procedure on the Characterization and Cytotoxicity of Reduced Graphene Oxide

The growing interest in graphene derivatives is a result of their variety of applications in many fields. Due to their use, the oral route could be a potential way of entrance for the general population. This work assesses the biotransformation of reduced graphene oxide (rGO) after an in vitro digestion procedure (mouth, gastric, intestinal, and colon digestion), and its toxic effects in different cell models (HepG2, Caco-2, and 3D intestinal model). The characterization of rGO digestas evidenced the agglomeration of samples during the in vitro gastrointestinal (g.i.) digestion. Internalization of rGO was only evident in Caco-2 cells exposed to the colonic phase and no cellular defects were observed. Digestas of rGO did not produce remarkable cytotoxicity in any of the experimental models employed at the tested concentrations (up to 200 µg/mL), neither an inflammatory response. Undigested rGO has shown cytotoxic effects in Caco-2 cells, therefore these results suggest that the digestion process could prevent the systemic toxic effects of rGO. However, additional studies are necessary to clarify the interaction of rGO with the g.i. tract and its biocompatibility profile.

Toxicological assessment of pristine and degraded forms of graphene functionalized with MnOx nanoparticles using human in vitro models representing different exposure routes

The development of novel advanced nanomaterials (NMs) with outstanding characteristics for their use in distinct applications needs to be accompanied by the generation of knowledge on their potential toxicological impact, in particular, that derived from different occupational risk exposure routes, such as inhalation, ingestion, and skin contact. The harmful effects of novel graphene-metal oxide composites on human health are not well understood, many toxicological properties have not been investigated yet. The present study has evaluated several toxicological effects associated with graphene decorated with manganese oxide nanoparticles (GNA15), in a comparative assessment with those induced by simple graphene (G2), on human models representing inhalation (A549 cell line), ingestion (HT29 cell line) and dermal routes (3D reconstructed skin). Pristine and degraded forms of these NMs were included in the study, showing to have different physicochemical and toxicological properties. The degraded version of GNA15 (GNA15d) and G2 (G2d) exhibited clear structural differences with their pristine counterparts, as well as a higher release of metal ions. The viability of respiratory and gastrointestinal models was reduced in a dose-dependent manner in the presence of both GNA15 and G2 pristine and degraded forms. Besides this, all NMs induced the production of reactive oxygen species (ROS) in both models. However, the degraded forms showed to induce a higher cytotoxicity effect. In addition, we found that none of the materials produced irritant effects on 3D reconstructed skin when present in aqueous suspensions. These results provide novel insights into the potentially harmful effects of novel multicomponent NMs in a comprehensive manner. Furthermore, the integrity of the NMs can play a role in their toxicity, which can vary depending on their composition and the exposure route.

Interactions of Graphene Oxide and Few-Layer Graphene with the Blood-Brain Barrier

Thanks to their biocompatibility and high cargo capability, graphene-based materials (GRMs) might represent an ideal brain delivery system. The capability of GRMs to reach the brain has mainly been investigated in vivo and has highlighted some controversy. Herein, we employed two in vitro BBB models of increasing complexity to investigate the bionano interactions with graphene oxide (GO) and few-layer graphene (FLG): a 2D murine Transwell model, followed by a 3D human multicellular assembloid, to mimic the complexity of the in vivo architecture and intercellular crosstalk. We developed specific methodologies to assess the translocation of GO and FLG in a label-free fashion and a platform applicable to any nanomaterial. Overall, our results show good biocompatibility of the two GRMs, which did not impact the integrity and functionality of the barrier. Sufficiently dispersed subpopulations of GO and FLG were actively uptaken by endothelial cells; however, the translocation was identified as a rare event.

Graphene oxide elicits microbiome-dependent type 2 immune responses via the aryl hydrocarbon receptor

The gut microbiome produces metabolites that interact with the aryl hydrocarbon receptor (AhR), a key regulator of immune homoeostasis in the gut1,2. Here we show that oral exposure to graphene oxide (GO) modulates the composition of the gut microbiome in adult zebrafish, with significant differences in wild-type versus ahr2-deficient animals. Furthermore, GO was found to elicit AhR-dependent induction of cyp1a and homing of lck+ cells to the gut in germ-free zebrafish larvae when combined with the short-chain fatty acid butyrate. To obtain further insights into the immune responses to GO, we used single-cell RNA sequencing to profile cells from whole germ-free embryos as well as cells enriched for lck. These studies provided evidence for the existence of innate lymphoid cell (ILC)-like cells3 in germ-free zebrafish. Moreover, GO endowed with a 'corona' of microbial butyrate triggered the induction of ILC2-like cells with attributes of regulatory cells. Taken together, this study shows that a nanomaterial can influence the crosstalk between the microbiome and immune system in an AhR-dependent manner.

Differential Radiosensitizing Effect of 50 nm Gold Nanoparticles in Two Cancer Cell Lines

Radiation therapy is widely used as an anti-neoplastic treatment despite the adverse effects it can cause in non-tumoral tissues. Radiosensitizing agents, which can increase the effect of radiation in tumor cells, such as gold nanoparticles (GNPs), have been described. To evaluate the radiosensitizing effect of 50 nm GNPs, we carried out a series of studies in two neoplastic cell lines, Caco2 (colon adenocarcinoma) and SKBR3 (breast adenocarcinoma), qualitatively evaluating the internalization of the particles, determining with immunofluorescence the number of γ-H2AX foci after irradiation with ionizing radiation (3 Gy) and evaluating the viability rate of both cell lines after treatment by means of an MTT assay. Nanoparticle internalization varied between cell lines, though they both showed higher internalization degrees for functionalized GNPs. The γ-H2AX foci counts for the different times analyzed showed remarkable differences between cell lines, although they were always significantly higher for functionalized GNPs in both lines. Regarding cell viability, in most cases a statistically significant decreasing tendency was observed when treated with GNPs, especially those that were functionalized. Our results led us to conclude that, while 50 nm GNPs induce a clear radiosensitizing effect, it is highly difficult to describe the magnitude of this effect as universal because of the heterogeneity found between cell lines.

Hazard assessment of abraded thermoplastic composites reinforced with reduced graphene oxide

Graphene-related materials (GRMs) are subject to intensive investigations and considerable progress has been made in recent years in terms of safety assessment. However, limited information is available concerning the hazard potential of GRM-containing products such as graphene-reinforced composites. In the present study, we conducted a comprehensive investigation of the potential biological effects of particles released through an abrasion process from reduced graphene oxide (rGO)-reinforced composites of polyamide 6 (PA6), a widely used engineered thermoplastic polymer, in comparison to as-produced rGO. First, a panel of well-established in vitro models, representative of the immune system and possible target organs such as the lungs, the gut, and the skin, was applied. Limited responses to PA6-rGO exposure were found in the different in vitro models. Only as-produced rGO induced substantial adverse effects, in particular in macrophages. Since inhalation of airborne materials is a key occupational concern, we then sought to test whether the in vitro responses noted for these materials would translate into adverse effects in vivo. To this end, the response at 1, 7 and 28 days after a single pulmonary exposure was evaluated in mice. In agreement with the in vitro data, PA6-rGO induced a modest and transient pulmonary inflammation, resolved by day 28. In contrast, rGO induced a longer-lasting, albeit moderate inflammation that did not lead to tissue remodeling within 28 days. Taken together, the present study suggests a negligible impact on human health under acute exposure conditions of GRM fillers such as rGO when released from composites at doses expected at the workplace.

MicroRNA-29b/graphene oxide–polyethyleneglycol–polyethylenimine complex incorporated within chitosan hydrogel promotes osteogenesis

MicroRNAs (miRNAs) play a pivotal role in regulating a number of physiologic and pathologic processes including bone marrow mesenchymal stem cell (BMSC) osteogenic differentiation, making them a candidate used to promote osteogenesis. However, due to intrinsic structure and characteristics, “naked” miRNAs are unstable in serum and could not pass across the cellular membrane. Nano delivery systems seem to be a solution to these issues. Recently, graphene oxide (GO)-based nanomaterials are considered to be promising for gene delivery due to their unique physiochemical characteristics such as high surface area, biocompatibility, and easy modification. In this work, a GO-based nanocomplex functionalized by polyethyleneglycol (PEG) and polyethylenimine (PEI) was prepared for loading and delivering miR-29b, which participates in multiple steps of bone formation. The nanocomplex revealed good biocompatibility, miRNA loading capacity, and transfection efficiency. The miR-29b/GO-PEG-PEI nanocomplex was capsulated into chitosan (CS) hydrogel for osteogenesis. In vitro and in vivo evaluation indicated that miR-29b/GO-PEG-PEI@CS composite hydrogel was able to promote BMSC osteogenic differentiation and bone regeneration. All these results indicate that PEG/PEI functionalized GO could serve as a promising candidate for miRNA cellular delivery, and the miR-29b/GO-PEG-PEI@CS hydrogel has the potential for repairing bone defects in vivo.

The Effect of Chronic Exposure of Graphene Nanoplates on the Viability and Motility of A549 Cells

Graphene and its derivatives are popular nanomaterials used worldwide in many technical fields and biomedical applications. Due to such massive use, their anticipated accumulation in the environment is inevitable, with a largely unknown chronic influence on living organisms. Although repeatedly tested in chronic in vivo studies, long-term cell culture experiments that explain the biological response to these nanomaterials are still scarce. In this study, we sought to evaluate the biological responses of established model A549 tumor cells exposed to a non-toxic dose of pristine graphene for eight weeks. Our results demonstrate that the viability of the A549 cells exposed to the tested graphene did not change as well as the rate of their growth and proliferation despite nanoplatelet accumulation inside the cells. In addition, while the enzymatic activity of mitochondrial dehydrogenases moderately increased in exposed cells, their overall mitochondrial damage along with energy production changes was also not detected. Conversely, chronic accumulation of graphene nanoplates in exposed cells was detected, as evidenced by electron microscopy associated with impaired cellular motility.

In vitro models and ex vivo systems used in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing gastrointestinal condition. Ulcerative colitis and Crohn’s disease are types of inflammatory bowel disease. Over many decades, the disease has been a topic of study, with experts still trying to figure out its cause and pathology. Researchers have established many in vivo animal models, in vitro cell lines, and ex vivo systems to understand its cause ultimately and adequately identify a therapy. However, in vivo animal models cannot be regarded as good models for studying IBD since they cannot completely simulate the disease. Furthermore, because species differences are a crucial subject of concern, in vitro cell lines and ex vivo systems can be employed to recreate the condition properly. In vitro models serve as the starting point for biological and medical research. Ex vivo and in vitro models for replicating gut physiology have been developed. This review aims to present a clear understanding of several in vitro and ex vivo models of IBD and provide insights into their benefits and limits and their value in understanding intestinal physiology.

Overview of potential adverse health effects of oral exposure to nanocellulose

Nanocellulose is an emerging material for which several food-related applications are foreseen, for example, novel food, functional food, food additive or in food contact materials. Nanocellulose materials can display a range of possible shapes (fibers, crystals), sizes and surface modifications. For food-related applications in the EU, information on the safety of substances must be assessed. The present review summarizes the current knowledge on (possible) adverse health effects of nanocellulose upon oral exposure, keeping EU regulatory aspects in mind. The overview indicates that toxicity data, especially from in vivo studies, are limited and outcomes are not unambiguous. The hazard assessment is further complicated by: the diversity in morphologies and surface modifications, lack of standard reference materials, limited knowledge about intestinal fate and absorption, analytical difficulties in biological matrices, dispersion issues, the possible presence of impurities and interferences within biological assays. Two subchronic in vivo toxicity studies show no indications of toxicity for two specific nanocellulose materials, even at high doses. However, these studies may have missed certain early or nano-specific toxic effects, such as inflammation potential, for which other, subacute studies provide some indications. Most in vitro studies show no cytotoxicity; however, several indicate that effects on oxidative stress and inflammatory responses depend on differences in size or surface treatments. Further, too few studies assessed genotoxicity of nanocelluloses. Therefore, immunotoxicity, oxidative stress and genotoxicity require further attention, as do absorption and effects on nutrient uptake. Recommendations for future research facilitating the safety assessment and safe-by-design of nanocellulose in food-related applications are provided.

Biological interactions of ferromagnetic iron oxide-carbon nanohybrids with alveolar epithelial cells

Iron oxide nanoparticles (IONPs) have been largely investigated in a plethora of biological fields for their interesting physical-chemical properties, which make them suitable for application in cancer therapy, neuroscience, and imaging. Several encouraging results have been reported in these contexts. However, the possible toxic effects of some IONP formulations can limit their applicability. In this work, IONPs were synthesized with a carbon shell (IONP@C), providing enhanced stability both as colloidal dispersion and in the biological environment. We conducted a careful multiparametric evaluation of IONP@C biological interactions in vitro, providing them with an in vivo-like biological identity. Our hybrid nanoformulation showed no cytotoxic effects on a widely employed model of alveolar epithelial cells for a variety of concentrations and exposure times. The IONP@C were efficiently internalized and TEM analysis allowed the protective role of the carbon shell against intracellular degradation to be assessed. Intracellular redistribution of the IONP@C from the lysosomes to the lamellar bodies was also observed after 72 hours.

Graphene oxide leads to mitochondrial-dependent apoptosis by activating ROS-p53-mPTP pathway in intestinal cells

Owing to its unique physical and chemical properties, graphene oxide (GO) has a wide range of applications in biomedical field. However, with the gradual improvement of biosafety investigations on nanomaterials, growing literatures have pointed out that GO could lead to oxidative stress, aggravation of inflammatory responses, and even irreversible lesions in human multi-tissues, while its damage to small intestinal remained unclear. In this study, we conducted an in-depth study on the toxicological effect of GO on intestinal tissues, and further clarified its toxic effect and molecular mechanism on inducing intestinal cell death. Firstly, we characterized the shape size, potential value, Fourier Transform infrared spectroscopy (FT-IR) characterization and pro-oxidant properties of GO nanosheets. The cytotoxicity of different concentrations of GO to Caco-2 and IEC-6 cell lines was thereafter observed, which was specifically manifested as invoking NADPH Oxidase 1 (NOX1) proteins, accompanied generation of reactive oxygen species (ROS). Since that, more p53 flowed into mitochondria to combine with cyclophilin D (CYPD), thus induced mitochondrial permeability transition pore (mPTP) opening. Through ROS-CyPD-mPTP signaling pathway, GO exerted imbalance of mitochondrial homeostasis, while released cytochrome c (CytC) would ultimate caspase-dependent cell apoptosis. In vivo experiment also confirmed that the microstructure of small intestine was damaged, and the apoptosis rate and oxidative markers were significantly increased in GO-treated Sprague- Dawley (SD) rats (40 mg/kg once every other day from day 1 to day 9 by oral gavage). Based on these findings, we conclude that the adverse effects of oral exposure of GO on the biological system mainly concentrate in the digestive tract, and clarify the key role of ROS-mitochondrial homeostasis-apoptosis axis in GO-derived intestinal toxicity. Considering all these results and the fact that GO exhibited intestinal toxicity, we believe that this research providing a safety reference for its biomedical applications.

Differential modulation of endothelial cytoplasmic protrusions after exposure to graphene-family nanomaterials

Engineered nanomaterials offer the benefit of having systematically tunable physicochemical characteristics (e.g., size, dimensionality, and surface chemistry) that highly dictate the biological activity of a material. Among the most promising engineered nanomaterials to date are graphene-family nanomaterials (GFNs), which are 2-D nanomaterials (2DNMs) with unique electrical and mechanical properties. Beyond engineering new nanomaterial properties, employing safety-by-design through considering the consequences of cell-material interactions is essential for exploring their applicability in the biomedical realm. In this study, we asked the effect of GFNs on the endothelial barrier function and cellular architecture of vascular endothelial cells. Using micropatterned cell pairs as a reductionist in vitro model of the endothelium, the progression of cytoskeletal reorganization as a function of GFN surface chemistry and time was quantitatively monitored. Here, we show that the surface oxidation of GFNs (graphene, reduced graphene oxide, partially reduced graphene oxide, and graphene oxide) differentially affect the endothelial barrier at multiple scales; from the biochemical pathways that influence the development of cellular protrusions to endothelial barrier integrity. More oxidized GFNs induce higher endothelial permeability and the increased formation of cytoplasmic protrusions such as filopodia. We found that these changes in cytoskeletal organization, along with barrier function, can be potentiated by the effect of GFNs on the Rho/Rho-associated kinase (ROCK) pathway. Specifically, GFNs with higher surface oxidation elicit stronger ROCK2 inhibitory behavior as compared to pristine graphene sheets. Overall, findings from these studies offer a new perspective towards systematically controlling the surface-dependent effects of GFNs on cytoskeletal organization via ROCK2 inhibition, providing insight for implementing safety-by-design principles in GFN manufacturing towards their targeted biomedical applications.

Factors affecting the biological response of Graphene

Nanotechnology has gained significant importance in different fields of medical, electronic, and environmental science. This technology is founded on the use of materials at the nanoscale scale (1-100 nanometers) for various purposes, particularly in the biomedical area, where its application is growing daily due to the need of materials with advanced properties. Over the past few years, there has been a growing use for graphene and its derivative composite materials. However, different physico-chemical properties influence its biological response; therefore, further studies to explain the interactions of these nanomaterials with biological systems are critical. This review presents the current advances in the applications of graphene in biomedicine with a focus on the physico-chemical characteristics of the graphene family and their influences on biological interactions.

Graphene oxide exacerbates dextran sodium sulfate-induced colitis via ROS/AMPK/p53 signaling to mediate apoptosis

Background

Graphene oxide (GO), a novel carbon-based nanomaterial, has promising applications in biomedicine. However, it induces potential cytotoxic effects on the gastrointestinal (GI) tract cells, and these effects have been largely uncharacterized. The present study aimed to explore the toxic effects of GO on the intestinal tract especially under pre-existing inflammatory conditions, such as inflammatory bowel disease (IBD), and elucidate underlying mechanisms.

Results

Our findings indicated that oral gavage of GO worsened acute colitis induced by 2.5% dextran sodium sulfate (DSS) in mice. In vitro, GO exacerbated DSS-induced inflammation and apoptosis in the FHC cell line, an ideal model of intestinal epithelial cells (IECs). Further, the potential mechanism underlying GO aggravated mice colitis and cell inflammation was explored. Our results revealed that GO treatment triggered apoptosis in FHC cells through the activation of reactive oxygen species (ROS)/AMP-activated protein kinase (AMPK)/p53 pathway, as evidenced by the upregulation of cytochrome c (Cytc), Bax, and cleaved caspase-3 (c-cas3) and the downregulation of Bcl-2. Interestingly, pretreatment with an antioxidant, N-acetyl-L-cysteine, and a specific inhibitor of AMPK activation, Compound C (Com.C), effectively inhibited GO-induced apoptosis in FHC cells.

Conclusions

Our data demonstrate that GO-induced IECs apoptosis via ROS/AMPK/p53 pathway activation accounts for the exacerbation of colitis in vivo and aggravation of inflammation in vitro. These findings provide a new insight into the pathogenesis of IBD induced by environmental factors. Furthermore, our findings enhance our understanding of GO as a potential environmental toxin, which helps delineate the risk of exposure to patients with disturbed intestinal epithelial barrier/inflammatory disorders such as IBD.

Investigating the effects of differently produced synthetic amorphous silica (E 551) on the integrity and functionality of the human intestinal barrier using an advanced in vitro co-culture model

E 551, also known as synthetic amorphous silica (SAS), is the second most produced food additive. However, according to the re-evaluation of E 551 by the European Food Safety Authority (EFSA) in 2018, the amount of available data on the oral toxicity of food grade E 551 is still insufficient for reliable risk assessment. To close this gap, this study aimed to investigate six food-grade SAS with distinct physicochemical properties on their interaction with the intestinal barrier using advanced in vitro intestinal co-cultures and to identify potential structure-activity relationships. A mucus-secreting Caco-2/HT-29/Raji co-culture model was treated with up to 50 µg/ml SAS for 48 h, which represents a dose range relevant to dietary exposure. No effects on cell viability, barrier integrity, microvilli function or the release of inflammatory cytokine were detected after acute exposure. Slight biological responses were observed for few SAS materials on iron uptake and gene expression levels of mucin 1 and G-protein coupled receptor 120 (GPR120). There was no clear correlation between SAS properties (single or combined) and the observed biological responses. Overall, this study provides novel insights into the short-term impact of food-relevant SAS with distinct characteristics on the intestinal epithelium including a range of intestine-specific functional endpoints. In addition, it highlights the importance of using advanced intestinal co-cultures embracing relevant cell types as well as a protective mucus barrier to achieve a comprehensive understanding of the biological response of food additives at the intestinal barrier in vitro.

Effects of Lipid-Based Encapsulation on the Bioaccessibility and Bioavailability of Phenolic Compounds

Phenolic compounds (quercetin, rutin, cyanidin, tangeretin, hesperetin, curcumin, resveratrol, etc.) are known to have health-promoting effects and they are accepted as one of the main proposed nutraceutical group. However, their application is limited owing to the problems related with their stability and water solubility as well as their low bioaccessibility and bioavailability. These limitations can be overcome by encapsulating phenolic compounds by physical, physicochemical and chemical encapsulation techniques. This review focuses on the effects of encapsulation, especially lipid-based techniques (emulsion/nanoemulsion, solid lipid nanoparticles, liposomes/nanoliposomes, etc.), on the digestibility characteristics of phenolic compounds in terms of bioaccessibility and bioavailability.

The impact of curcumin-graphene based nanoformulation on cellular interaction and redox-activated apoptosis: An in vitro colon cancer study

Natural plants derivatives have gained enormous merits in cancer therapy applications upon formulation with nanomaterials. Curcumin, as a popular research focus has acquired such improvements surpassing its disadvantageous low bioavailability. To this point, the available research data had confirmed the importance of nanomaterial type in orienting cellular response and provoking different toxicological and death mechanisms that may range from physical membrane damage to intracellular changes. This in turn underlines the poorly studied field of nanoformulation interaction with cells as the key determinant in toxicology outcomes. In this work, curcumin-AuNPs-reduced graphene oxide nanocomposite (CAG) was implemented as a model, to study the impact on cellular membrane integrity and the possible redox changes using colon cancer in vitro cell lines (HT-29 and SW-948), representing drug-responsive and resistant subtypes. Morphological and biochemical methods of transmission electron microscopy (TEM), apoptosis assay, reactive oxygen species (ROS) and antioxidants glutathione and superoxide dismutase (GSH and SOD) levels were examined with consideration to suitable protocols and vital optimizations. TEM micrographs proved endocytic uptake with succeeding cytoplasm deposition, which unlike other nanomaterials studied previously, conserved membrane integrity allowing intracellular cytotoxic mechanism. Apoptosis was confirmed with gold-standard morphological features observed in micrographs, while redox parameters revealed a time-dependent increase in ROS accompanied with regressive GSH and SOD levels. Collectively, this work demonstrates the success of graphene as a platform for curcumin intracellular delivery and cytotoxicity, and further highlights the importance of suitable in vitro methods to be used for nanomaterial validation.

The impact of synthetic amorphous silica (E 551) on differentiated Caco-2 cells, a model for the human intestinal epithelium

For several decades, food-grade synthetic amorphous silica (SAS) have been used as a technological additive to reduce caking of food powders. Human exposure is thus inevitable and safety concerns are taken seriously. The toxicity of silica in general and SAS in particular has been studied extensively. Overall, there is little evidence that food-grade SAS pose any health risks to humans. However, from the available data it was often not clear which type of silica was used. Accordingly, the latest report of the European food safety authority requested additional toxicity data for well-characterised "real food-grade SAS". To close this gap, we screened a panel of ten well-defined, food-grade SAS for potential adverse effects on differentiated Caco-2 cells. Precipitated and fumed SAS with low, intermediate and high specific surface area were included to determine structure-activity relationships. In a physiological dose-range up to 50 μg/ml and 48 h of incubation, none of the materials induced adverse effects on differentiated Caco-2 cells. This held true for endpoints of acute cytotoxicity as well as epithelial specific measures of barrier integrity. These results showed that despite considerable differences in production routes and material characteristics, food-relevant SAS did not elicit acute toxicity responses in intestinal epithelial cells.

Synthesis and Physicochemical Transformations of Size-Sorted Graphene Oxide during Simulated Digestion and Its Toxicological Assessment against an In Vitro Model of the Human Intestinal Epithelium

In the last decade, along with the increasing use of graphene oxide (GO) in various applications, there is also considerable interest in understanding its effects on human health. Only a few experimental approaches can simulate common routes of exposure, such as ingestion, due to the inherent complexity of the digestive tract. This study presents the synthesis of size-sorted GO of sub-micrometer- or micrometer-sized lateral dimensions, its physicochemical transformations across mouth, gastric, and small intestinal simulated digestions, and its toxicological assessment against a physiologically relevant, in vitro cellular model of the human intestinal epithelium. Results from real-time characterization of the simulated digestas of the gastrointestinal tract using multi-angle laser diffraction and field-emission scanning electron microscopy show that GO agglomerates in the gastric and small intestinal phase. Extensive morphological changes, such as folding, are also observed on GO following simulated digestion. Furthermore, X-ray photoelectron spectroscopy reveals that GO presents covalently bound N-containing groups on its surface. It is shown that the GO employed in this study undergoes reduction. Toxicological assessment of the GO small intestinal digesta over 24 h does not point to acute cytotoxicity, and examination of the intestinal epithelium under electron microscopy does not reveal histological alterations. Both sub-micrometer- and micrometer-sized GO variants elicit a 20% statistically significant increase in reactive oxygen species generation compared to the untreated control after a 6 h exposure.

Nanostructure generation during milk digestion in presence of a cell culture model simulating the small intestine

HYPOTHESIS

The development of advanced oral delivery systems for bioactive compounds requires the fundamental understanding of the digestion process within the gastrointestinal tract. Towards this goal, dynamic invitro digestion models, capable of characterising the molecular as well as colloidal aspects of food, together with their biological interactions with relevant invitro cell culture models, are essential.

EXPERIMENTS

In this study, we demonstrate a novel digestion model that combines flow-through time resolved small angle X-ray scattering (SAXS) with an invitro Caco-2/HT-29 cell co-culture model that also contained a mucus layer. This set-up allows the dynamic insitu characterisation of colloidal structures and their transport across a viable intestinal cell layer during simulated digestion.

FINDINGS

An integrated online SAXS - invitro cell co-culture model was developed and applied to study the digestion of nature's own emulsion, milk. The impact of the invitro cell culture on the digestion-triggered formation and evolution of highly ordered nanostructures in milk is demonstrated. Reported is also the crucial role of the mucus layer on top of the cell layer, protecting the cells from degradation by digestive juice components such as lipase. The novel model can open unique possibilities for the dynamic investigation of colloidal structure formation during lipid digestion and their effect on the uptake of bioactive molecules by the cells.

Interactions of graphene oxide and graphene nanoplatelets with the in vitro Caco-2/HT29 model of intestinal barrier

Carbon-based nanomaterials are being increasingly used, demanding strong information to support their safety in terms of human health. As ingestion is one of the most important exposure routes in humans, we have determined their potential risk by using an in vitro model simulating the human intestinal barrier and evaluated the effects of both graphene oxide (GO) and graphene nanoplatelets (GNPs). A coculture of differentiated Caco-2/HT29 cells presenting inherent intestinal epithelium characteristics (i.e. mucus secretion, brush border, tight junctions, etc.) were treated with GO or GNPs for 24 h. Different endpoints such as viability, membrane integrity, NPs localization, cytokines secretion, and genotoxic damage were evaluated to have a wide view of their potentially harmful effects. No cytotoxic effects were observed in the cells that constitute the barrier model. In the same way, no adverse effects were detected neither in the integrity of the barrier (TEER) nor in its permeability (LY). Nevertheless, a different bio-adhesion and biodistribution behavior was observed for GO and GNPs by confocal microscopy analysis, with a more relevant uptake of GNPs. No oxidative damage induction was detected, either by the DCFH-DA assay or the FPG enzyme in the comet assay. Conversely, both GO and GNPs were able to induce DNA breaks, as observed in the comet assay. Finally, low levels of anti-inflammatory cytokines were detected, suggesting a weak anti-inflammatory response. Our results show the moderate/severe risk posed by GO/GNPs exposures, given the observed genotoxic effects, suggesting that more extensive genotoxic evaluations must be done to properly assess the genotoxic hazard of these nanomaterials.

Graphene oxide effects in early ontogenetic stages of Triticum aestivum L. seedlings

Nanomaterials are being used increasingly in various areas such as electronic devices manufacture, medicine, mechanical devices production, and even food industry. Therefore, the evaluation of their toxicity is mandatory. Graphene oxide (GO) has been shown to have both positive as well as negative impact on different crop plants, depending on species, dose, and duration of exposure. The current study evaluated the impact of GO sheets at different concentrations (500, 1000 and 2000 mg/L) on physiological, biochemical and genetic levels to determine the possible toxic action. Wheat caryopses were treated with GO for 48 h and 7 days. The germination rate and roots elongation decreased in a dose-response manner, except the sample treated with GO at a concentration of 1000 mg/L. Mitotic index has ascendant trend; its increase may be due to the accumulation of prophases GO induced significant accumulation of the cells with aberrations, their presence suggests a clastogenic/aneugenic effect of these carbon nanomaterials. Regarding enzymatic and non-enzymatic antioxidant system defence, the activity varied depending on the dose of GO. Thus, chlorophyll a pigments content decreased significantly at high dose (2000 mg/L), while the carotenoid pigments had lower content at 500 mg/L of GO, and no statistical difference encountered in case of chlorophyll b amount. The antioxidant enzyme activity (CAT, POD, and SOD) was higher at low dose of GO, indicating the presence of oxidative stress generated as a response to the GO treatment. Also, the free radical scavenging activity of the polyphenolic compounds was enhanced upon GO exposure. The GO accumulation has been identified by transmission electron microscopy only at plumules level, near the intercellular space.

MoS2 flakes stabilized with DNA/RNA nucleotides: In vitro cell response

Two-dimensional transition metal dichalcogenides (TMDCs), such as MoS₂ and WS₂, have recently emerged as nanomaterials with potential use in biomedicine. An attractive means to favor their interaction with biological media is the use of proper biomolecules as exfoliating/dispersing agents. Here, MoS₂ flakes were stabilized with different small functional biomolecules such as adenosine monophosphate (AMP), guanosine monophosphate (GMP) and flavin mononucleotide (FMN) through the strong nucleotide-MoS₂ interaction of Lewis acid-base type, rather than just on the weak dispersive and hydrophobic forces commonly associated with the use of many surfactants. The impact of the nucleotide-stabilized MoS₂ flakes on the viability and cell proliferation, on the production of intracellular reactive oxygen species (ROS), and on the preosteoblast differentiation process (early stage) has been also evaluated, as well as the incorporation and intracellular localization of the nanomaterials by MC3T3-E1 and Saos-2 cells. The nucleotide-stabilized MoS₂ flakes were found to exhibit excellent biocompatibility. Furthermore, their incorporation did not affect the integrity of the cell plasma membrane, which makes them ideal candidates for delivering drug/gene directly into cells. The in vitro cell response of tumor cells to these nanomaterials differs from that of undifferentiated cells, which provides the basis for their potential use in cancer therapy.

Safety Assessment of Graphene-Based Materials: Focus on Human Health and the Environment

Graphene and its derivatives are heralded as "miracle" materials with manifold applications in different sectors of society from electronics to energy storage to medicine. The increasing exploitation of graphene-based materials (GBMs) necessitates a comprehensive evaluation of the potential impact of these materials on human health and the environment. Here, we discuss synthesis and characterization of GBMs as well as human and environmental hazard assessment of GBMs using in vitro and in vivo model systems with the aim to understand the properties that underlie the biological effects of these materials; not all GBMs are alike, and it is essential that we disentangle the structure-activity relationships for this class of materials.

Highly hydrophilic carbon nanoparticles: uptake mechanism by mammalian and plant cells

As one of the carbon based materials, the potential application of carbon nanoparticles (CNPs) has emerged in the promotion of plant growth. However, knowledge on the biological mechanism of how the CNPs interact with plant cells is limited. In this study, nanostructures of CNPs were examined. The particles exhibited particulate morphology and their size distribution was in the range of 18 to 70 nm, with an average size of 30 nm. Hydrophilic groups of COOH and OH were present on the surface of CNPs, and CNPs showed the common feature of graphitic sp2 hybridization carbons. The CNPs were determined to be biocompatible with these two cell lines, mammalian cells (A549 cells) and plant cells (BY-2 cells). The COOH groups on the surface of CNPs were functionalized via covalent binding with a fluorescent dye for improvement of the fluorescence. The fluorescent carbon nanoparticles (FCNPs) were found to cross the cell membrane and enter cells (A549 cells and BY-2 cells) in an energy-dependent manner. Subsequently, the mechanism of FCNPs interaction with the cell membrane was evaluated in the presence of inhibitors that specifically affect different endocytosis membrane proteins. The FCNPs mainly entered A549 cells through caveolin-mediated endocytosis and macropinocytosis, and clathrin-dependent endocytosis was also involved in the transportation of the FCNPs. Clathrin-independent endocytosis mediated in the internalization of FCNPs in BY-2 cells. The way FCNPs entering cells will provide a fundamental understanding of the influence of CNPs on cell membrane.

Laser Ablation as a Versatile Tool To Mimic Polyethylene Terephthalate Nanoplastic Pollutants: Characterization and Toxicology Assessment

The presence of micro- and nanoplastics in the marine environment is raising strong concerns since they can possibly have a negative impact on human health. In particular, the lack of appropriate methodologies to collect the nanoplastics from water systems imposes the use of engineered model nanoparticles to explore their interactions with biological systems, with results not easily correlated with the real case conditions. In this work, we propose a reliable top-down approach based on laser ablation of polymers to form polyethylene terephthalate (PET) nanoplastics, which mimic real environmental nanopollutants, unlike synthetic samples obtained by colloidal chemistry. PET nanoparticles were carefully characterized in terms of chemical/physical properties and stability in different media. The nanoplastics have a ca. 100 nm average dimension, with significant size and shape heterogeneity, and they present weak acid groups on their surface, similarly to photodegraded PET plastics. Despite no toxic effects emerging by in vitro studies on human Caco-2 intestinal epithelial cells, the formed nanoplastics were largely internalized in endolysosomes, showing intracellular biopersistence and long-term stability in a simulated lysosomal environment. Interestingly, when tested on a model of intestinal epithelium, nano-PET showed high propensity to cross the gut barrier, with unpredictable long-term effects on health and potential transport of dispersed chemicals mediated by the nanopollutants.

Biotransformation and Biological Interaction of Graphene and Graphene Oxide during Simulated Oral Ingestion

The biotransformation and biological impact of few layer graphene (FLG) and graphene oxide (GO) are studied, following ingestion as exposure route. An in vitro digestion assay based on a standardized operating procedure (SOP) is exploited. The assay simulates the human ingestion of nanomaterials during their dynamic passage through the different environments of the gastrointestinal tract (salivary, gastric, intestinal). Physical-chemical changes of FLG and GO during digestion are assessed by Raman spectroscopy. Moreover, the effect of chronic exposure to digested nanomaterials on integrity and functionality of an in vitro model of intestinal barrier is also determined according to a second SOP. These results show a modulation of the aggregation state of FLG and GO nanoflakes after experiencing the complex environments of the different digestive compartments. In particular, chemical doping effects are observed due to FLG and GO interaction with digestive juice components. No structural changes/degradation of the nanomaterials are detected, suggesting that they are biopersistent when administered by oral route. Chronic exposure to digested graphene does not affect intestinal barrier integrity and is not associated with inflammation and cytotoxicity, though possible long-term adverse effects cannot be ruled out.

In vitro and environmental toxicity of reduced graphene oxide as an additive in automotive lubricants

Despite the ground-breaking potential of nanomaterials, their safe and sustainable incorporation into an array of industrial markets prompts a deep and clear understanding of their potential toxicity for both humans and the environment. Among the many materials with great potential, graphene has shown promise in a variety of applications; however, the impact of graphene based products on living systems remains poorly understood. In this paper, we illustrate that via exploiting the tribological properties of graphene nanosheets, we can successfully improve both the frictional behaviour and the anti-wear capacity of lubricant oil for mechanical transmission. By virtue of reducing friction and enhancing lubricant lifetimes, we can forecast a reduction in friction based energy loss, in addition to a decrease in the carbon footprint of vehicles. The aforementioned positive environmental impact is further strengthened considering the lack of acute toxicity found in our extensive in vitro investigation, in which both eukaryotic and prokaryotic cells were tested. Collectively, our body of work suggests that by the use of safe nanoadditives we could contribute to reducing the environmental impact of transportation and therein take a positive step towards a more sustainable automotive sector. The workflow proposed here for the evaluation of human and environmental toxicity will allow for the study of nanosized bare graphene material and can be broadly applied to the translation of graphene-based nanomaterials into the market.

Rhombic organization of microvilli domains found in a cell model of the human intestine

Symmetry is rarely found on cellular surfaces. An exception is the brush border of microvilli, which are essential for the proper function of transport epithelia. In a healthy intestine, they appear densely packed as a 2D-hexagonal lattice. For in vitro testing of intestinal transport the cell line Caco-2 has been established. As reported by electron microscopy, their microvilli arrange primarily in clusters developing secondly into a 2D-hexagonal lattice. Here, atomic force microscopy (AFM) was employed under aqueous buffer conditions on Caco-2 cells, which were cultivated on permeable filter membranes for optimum differentiation. For analysis, the exact position of each microvillus was detected by computer vision; subsequent Fourier transformation yielded the type of 2D-lattice. It was confirmed, that Caco-2 cells can build a hexagonal lattice of microvilli and form clusters. Moreover, a second type of arrangement was discovered, namely a rhombic lattice, which appeared at sub-maximal densities of microvilli with (29 ± 4) microvilli / μm². Altogether, the findings indicate the existence of a yet undescribed pattern in cellular organization.