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Current analyses show a widespread occurrence of microplastic particles in food products and raise the question of potential risks to human health. Plastic particles are widely considered to be inert due to their low chemical reactivity and therefore supposed to pose, if at all only minor hazards. However, variable physicochemical conditions during the passage of the gastrointestinal tract gain strong importance, as they may affect particle characteristics. This study aims to analyze the impact of the gastrointestinal passage on the physicochemical particle characteristics of the five most produced and thus environmentally relevant plastic materials polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate and polystyrene. Scanning electron microscopy (SEM) and subsequent image analysis were employed to characterize microplastic particles. Our results demonstrate a high resistance of all plastic particles to the artificial digestive juices. The present results underline that the main stages of the human gastrointestinal tract do not decompose the particles. This allows a direct correlation between the physicochemical particle characteristics before and after digestion. Special attention must be paid to the adsorption of organic compounds like proteins, mucins and lipids on plastic particles since it could lead to misinterpretations of particle sizes and shapes.
The elucidation of mechanisms underlying the cellular uptake of nanoparticles (NPs) is an important topic in nanotoxicological research. Most studies dealing with silver NP uptake provide only qualitative data about internalization efficiency and do not consider NP-specific dosimetry. Therefore, we performed a comprehensive comparison of the cellular uptake of differently coated silver NPs of comparable size in different human intestinal Caco-2 cell-derived models to cover also the influence of the intestinal mucus barrier and uptake-specialized M-cells. We used a combination of the Transwell system, transmission electron microscopy, atomic absorption spectroscopy, and ion beam microscopy techniques. The computational in vitro sedimentation, diffusion, and dosimetry (ISDD) model was used to determine the effective dose of the particles in vitro based on their individual physicochemical characteristics. Data indicate that silver NPs with a similar size and shape show coating-dependent differences in their uptake into Caco-2 cells. The internalization of silver NPs was enhanced in uptake-specialized M-cells while the mucus did not provide a substantial barrier for NP internalization. ISDD modeling revealed a fivefold underestimation of dose–response relationships of NPs in in vitro assays. In summary, the present study provides dosimetry-adjusted quantitative data about the influence of NP coating materials in cellular uptake into human intestinal cells. Underestimation of particle effects in vitro might be prevented by using dosimetry models and by considering cell models with greater proximity to the in vivo situation, such as the M-cell model.
Size and shape are crucial parameters which have impact on the potential of nanoparticles to penetrate cell membranes and epithelial barriers. Current research in nanotoxicology additionally focuses on particle coating. To distinguish between core- and coating-related effects in nanoparticle uptake and translocation, two nanoparticles equal in size, coating and charge but different in core material were investigated.
Silver and iron oxide nanoparticles coated with poly(acrylic acid) were chosen and extensively characterized by small-angle x-ray scattering, nanoparticle tracing analysis and transmission electron microscopy (TEM). Uptake and transport were studied in the intestinal Caco-2 model in a Transwell System with subsequent elemental analysis. TEM and ion beam microscopy were conducted for particle visualization.
Although equal in size, charge and coating, the behavior of the two particles in Caco-2 cells was different: while the internalized amount was comparable, only iron oxide nanoparticles additionally passed the epithelium. Our findings suggest that the coating material influenced only the uptake of the nanoparticles whereas the translocation was determined by the core material.
Knowledge about the different roles of the particle coating and core materials in crossing biological barriers will facilitate toxicological risk assessment of nanoparticles and contribute to the optimization of pharmacokinetic properties of nano-scaled pharmaceuticals.