Engineered Nanoparticles as Potential Food Contaminants and Their Toxicity to Caco-2 Cells

Safe nanomaterials: from their use, application, and disposal to regulations

Nanomaterials are structures with a wide range of applications in the medical, pharmaceutical, food, textile, and electronic industries, reaching more customers worldwide. As a relatively new technological field, the information about the associated risk of nanomaterials in environmental and human health must be addressed and consolidated to develop accurate legislations, frameworks, and guidelines to standardise their use in any field. This review aims to display and context the global applications of nanomaterials, their final disposal, as well as the perspective of the current efforts formulated by various countries (including Mexico and Latin American countries), international official departments and organisations directed to implement regulations on nanomaterials, nanotechnology, and nanoscience matters. In addition, the compiled information includes the tools, initiatives, and strategies to develop regulatory frameworks, such as life cycle assessments, risk assessments, technical tools, and biological models to evaluate their effects on living organisms. Finally, the authors point out the importance of implementing global regulations to promote nanotechnological research according to a precautionary principle focused on an environmental and health protection approach to ensure the use and application of nanotechnologies safely, and responsibly.

Comparative study of the transcriptomes of Caco-2 cells cultured under dynamic vs. static conditions following exposure to titanium dioxide and zinc oxide nanomaterials

Due to the widespread application of food-relevant inorganic nanomaterials, the gastrointestinal tract is potentially exposed to these materials. Gut-on-chip in vitro systems are proposed for the investigation of compound toxicity as they better recapitulate the in vivo human intestinal environment than static models, due to the added shear stresses associated with the flow of the medium. We aimed to compare cellular responses of intestinal epithelial Caco-2 cells at the gene expression level upon TiO₂ (E171) and ZnO (NM110) nanomaterial exposure when cultured under dynamic and conventionally applied static conditions. Whole-genome transcriptome analyses upon exposure of the cells to TiO₂ and ZnO nanomaterials revealed differentially expressed genes and related biological processes that were culture condition specific. The total number of differentially expressed genes (p < 0.01) and affected pathways (p < 0.05 and FDR < 0.25) after nanomaterial exposure was higher under dynamic culture conditions than under static conditions for both nanomaterials. The observed increase in nanomaterial-induced responses in the gut-on-chip model indicates that shear stress might be a major factor in cell susceptibility. This is the first report on the application of a gut-on-chip system in which gene expression responses upon TiO₂ and ZnO nanomaterial exposure are evaluated and compared to a static system. It extends current knowledge on nanomaterial toxicity assessment and the influence of a dynamic environment on cellular responses. Application of the gut-on-chip system resulted in higher sensitivity of the cells and might thus be an attractive system for use in the toxicological hazard characterization of nanomaterials.

Protective Role of Flavonoids against Intestinal Pro-Inflammatory Effects of Silver Nanoparticles

Silver nanoparticles (AgNP) have been increasingly incorporated into food-related and hygiene products for their unique antimicrobial and preservative properties. The consequent oral exposure may then result in unpredicted harmful effects in the gastrointestinal tract (GIT), which should be considered in the risk assessment and risk management of these materials. In the present study, the toxic effects of polyethyleneimine (PEI)-coated AgNP (4 and 19 nm) were evaluated in GIT-relevant cells (Caco-2 cell line as a model of human intestinal cells, and neutrophils as a model of the intestinal inflammatory response). This study also evaluated the putative protective action of dietary flavonoids against such harmful effects. The obtained results showed that AgNP of 4 and 19 nm effectively induced Caco-2 cell death by apoptosis with concomitant production of nitric oxide, irrespective of the size. It was also observed that AgNP induced human neutrophil oxidative burst. Interestingly, some flavonoids, namely quercetin and quercetagetin, prevented the deleterious effects of AgNP in both cell types. Overall, the data of the present study provide a first insight into the promising protective role of flavonoids against the potentially toxic effects of AgNP at the intestinal level.

Antimicrobial Properties of Food Nanopackaging: A New Focus on Foodborne Pathogens

Food products contaminated by foodborne pathogens (bacteria, parasites, and viruses) cause foodborne diseases. Today, great efforts are being allocated to the development of novel and effective agents against food pathogenic microorganisms. These efforts even might have a possible future effect in coronavirus disease 2019 (COVID-19) pandemic. Nanotechnology introduces a novel food packaging technology that creates and uses nanomaterials with novel physiochemical and antimicrobial properties. It could utilize preservatives and antimicrobials to extend the food shelf life within the package. Utilizing the antimicrobial nanomaterials into food packaging compounds typically involves incorporation of antimicrobial inorganic nanoparticles such as metals [Silver (Ag), Copper (Cu), Gold (Au)], and metal oxides [Titanium dioxide (TiO2), Silicon oxide (SiO2), Zinc oxide (ZnO)]. Alternatively, intelligent food packaging has been explored for recognition of spoilage and pathogenic microorganisms. This review paper focused on antimicrobial aspects of nanopackaging and presented an overview of antibacterial properties of inorganic nanoparticles. This article also provides information on food safety during COVID-19 pandemic.

The Current Understanding of Autophagy in Nanomaterial Toxicity and Its Implementation in Safety Assessment-Related Alternative Testing Strategies

Nanotechnology has rapidly promoted the development of a new generation of industrial and commercial products; however, it has also raised some concerns about human health and safety. To evaluate the toxicity of the great diversity of nanomaterials (NMs) in the traditional manner, a tremendous number of safety assessments and a very large number of animals would be required. For this reason, it is necessary to consider the use of alternative testing strategies or methods that reduce, refine, or replace (3Rs) the use of animals for assessing the toxicity of NMs. Autophagy is considered an early indicator of NM interactions with cells and has been recently recognized as an important form of cell death in nanoparticle-induced toxicity. Impairment of autophagy is related to the accelerated pathogenesis of diseases. By using mechanism-based high-throughput screening in vitro, we can predict the NMs that may lead to the generation of disease outcomes in vivo. Thus, a tiered testing strategy is suggested that includes a set of standardized assays in relevant human cell lines followed by critical validation studies carried out in animals or whole organism models such as C. elegans (Caenorhabditis elegans), zebrafish (Danio rerio), and Drosophila (Drosophila melanogaster)for improved screening of NM safety. A thorough understanding of the mechanisms by which NMs perturb biological systems, including autophagy induction, is critical for a more comprehensive elucidation of nanotoxicity. A more profound understanding of toxicity mechanisms will also facilitate the development of prevention and intervention policies against adverse outcomes induced by NMs. The development of a tiered testing strategy for NM hazard assessment not only promotes a more widespread adoption of non-rodent or 3R principles but also makes nanotoxicology testing more ethical, relevant, and cost- and time-efficient.

Influence of the stabilizers on the toxicity of metallic nanomaterials in aquatic organisms and human cell lines

In this study, following a systematic approach, we used aquatic species (bacteria Vibrio fischeri and microalgae Raphidocelis subcapitata) and different human cell lines (Caco-2, HepG2, SV-80 and HaCaT) representing different tissues and exposure pathways, to investigate how two organic stabilizers (PVA and DMSO) used for NMs dispersion influence their physicochemical properties, the persistence of metals in suspension and the toxicity/ecotoxicity of two metallic NMs (nano-Ag and nano-Cu). Although the stabilizers are expected to contribute to improve the dispersion and stability of NMs, the results obtained clearly showed that no similar changes in toxicity and morphological properties of the nano-Ag can be expected after its stabilization with PVA. Thus, regarding human cell lines, the reduction in the average size of the PVA-nano-Ag was followed by a reduction or maintenance of its toxicity, but the opposite was observed for the aquatic species tested since an increase in the average size enhanced its toxicity. As far as nano-Cu is considered DMSO contributed for a better dispersion of this nanomaterial, however this was not translated in a similar toxicity/ecotoxicity modification. In summary, even for nano-Cu, for which few or no data exists regarding its toxicity after stabilization with organic compounds, it was confirmed with consistent data, that the toxicity of metallic NMs is a complex combination of average size, chemical composition, solubilization or persistence in suspension of the metallic forms, interaction with test medium components and sensitivity of test species and cell lines. The combination of all of these factors makes the toxicity of metallic NMs unpredictable and points for the need of an extensive evaluation of each new formulation.

Potential adverse effects of engineered nanomaterials commonly used in food on the miRNome

The emergence of nanotechnology has greatly impacted our daily lives. Multiple products, including cosmetics, pharmaceuticals, electronics and food, are produced with incorporation of nanomaterials (NMs). Nanotechnology has yielded many promising benefits, yet, there remains much uncertainty about the hazards of NMs to humans. Hence, it is important to ensure safety of the users. Although many in vitro and in vivo studies have been carried out on the potential toxicity generated by NMs in food, its effects on the microRNA genome (miRNome) involved in the regulation of gene expression have been poorly understood. Therefore, this review focuses on the types of commonly used NMs (containing silicon dioxide, titanium dioxide, silver or zinc oxide) in food products and their potential toxic effects, including how NMs can induce epigenetic toxicity mediated via altered miRNA expression.