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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 utilization of silver nanoparticles in consumer related products has significantly increased over the last decade, especially due to their antimicrobial properties. Today they are used in a high variety of products ranging from food containers over children toys and textiles. Therefore, research on the toxicological potential of silver nanoparticles becomes increasingly important for a high amount of studies. Unfortunately, the results of these studies are extremely diverse and do not lead to a consistent evaluation. The central problem lies in the use of a wide range of silver nanoparticles, which show a broad size distribution. To overcome this problem we report on the synthesis and application of small silver nanoparticles with a narrow size distribution (R = 3.1 nm, σ = 0.6 nm). The poly(acrylic acid) stabilized particles are thoroughly characterized by small-angle X-ray scattering, dynamic light scattering and UV/Vis spectroscopy. The particles are highly stable and show no aggregation for more than six months. It is foreseen to use these thoroughly characterized nanoparticles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. As a first step the particles are used in the first world-wide inter-laboratory comparison of SAXS. Furthermore, the stabilizing ligand PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione (GSH) and bovine serum albumin (BSA) have been performed as examples. With this flexible system first applications regarding biological application in an artificial digestion procedure have been performed. Thereby the changes in size distribution and aggregation state were monitored by SAXS. Additionally these particles show a high catalytic activity of (436 ± 24) L g-1 s-1 in the reduction of 4- nitrophenol to 4-aminophenol. This activity is two orders of magnitude higher than for other silver particles in the literature.
An artificial digestion of silver nitrate is reported. It is shown that AgSCN nanoparticles emerge from ionic silver in saliva and remain present during the entire digestion process. The particles were characterized by infrared spectroscopy and small- and wide-angle X-ray scattering (SAXS/WAXS) regarding their composition and size distribution.
Over the last decade nanoparticles are progressively included in products of our daily life. Due to their antimicrobial properties, silver nanoparticles are used in a high variety of consumer products ranging from food containers over medicine and textiles. Therefore, research on the toxicological potential of nanosilver becomes increasingly important. This includes investigations concerning uptake, distribution and excretion of the particles. However, little attention was paid to changes of physical and chemical properties of the particles in the human body. One of the most important questions is if the particles can pass the digestion process without altering their shape and size. In this study we report on a versatile system of ultra-small silver nanoparticles with a mean volume weighted radius of 3.1 nm and a narrow size distribution width of 20%. The nanoparticles’ coating of poly (acrylic acid) can easily be exchanged by biocompatible ligands like albumin or glutathione. The particles are thoroughly characterized by small angle X-ray scattering (SAXS), DLS, IR and UV/Vis spectroscopy. We used the particles in an artificial digestion procedure which mimics the gastro-intestinal passage (Figure 1). Thereby the changes in the size distribution during the digestion process were analytically monitored by SAXS. Additionally, we used as food components oil, starch, skimmed milk powder and mixture thereof to provide a preferably realistic environment. Large aggregates of up to 56 nm were formed in the absence of food additives. In contrast, the presence of oil and starch limit the radii of aggregates to about 10 nm. Milk powder shows strong protective properties resulting in only small aggregates of 6 nm radii. Our results indicate that silver can indeed pass the digestion process in a nanoscale form depending on the nanoparticle coating and additional ingredients. These results have an impact on future toxicological considerations regarding silver nanoparticle-containing consumer products.
Creating the Silver Standard: Development of a Silver Nanoparticle Reference Material using SAXS
(2017)
The utilization of silver nanoparticles in consumer related products has significantly increased over the last decade, especially due to their antimicrobial properties. Today they are used in a high variety of products, which ranges from food containers over children toys and textiles. Therefore, research on the toxicological potential of silver in a nanoscale form becomes increasingly important for a high amount of studies. Unfortunately the results of these studies are extremely diverse and do not lead to a consistent evaluation of the toxicity of silver nanoparticles. The central problem lies in the use of a wide range of silver nanoparticles, which show a broad size distribution. To overcome this problem we report on the synthesis of ultra-small silver nanoparticles and their quantitative characterization by small-angle X-ray scattering. The particles are highly stable and show no aggregation for more than six months. SAXS analysis via a Monte Carlo data evaluation procedure reveal a narrow size distribution of the silver cores with a mean volume weighted radius of 3.0 nm and a distribution width of 0.6 nm. Dynamic light scattering provides a hydrodynamic radius of 10.0 nm and a PDI of 0.09. The particles are stabilized with poly(acrylic acid) (PAA) forming a shell with a thickness of 7.0 nm. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. As a first step the particles are used in the first world-wide inter-laboratory comparison of SAXS. This study reveals that SAXS shows highly reproducible results for particles in the sub-20 nm region independently on the type of instrument used. Furthermore, the stabilizing ligand PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione (GSH) and bovine serum albumin (BSA) have been performed as examples. With this flexible system first applications regarding biological application in an artificial digestion procedure have been performed. Thereby the changes in size distribution and aggregation state were monitored by SAXS.
Aluminum is the third most abundant element in the earth crust and therefore ubiquitously detectable in the environment. Mostly found in the form of derivatives such as silicates or oxides, it also occurs as metallic aluminum for example as colorant in sweets or in aluminum foil.
With regard to potential toxicological effects, the different solubility of metallic aluminum nanoparticles compared to Al2O3 is of high relevance. Formation of ions may facilitate the crossing of blood-tissue barriers. Distribution towards other organs and subsequent re-formation of particulate aluminum due to milieu changes might occur. Therefore, the determination of solubility is required for proper risk assessment. Inductively coupled plasma mass spectrometry (ICP-MS) allows determination of aluminum with a detection limit of about 6 ppb. It could be proven that dissolution and solubility of metallic aluminum is significantly different when compared to Al2O3.
Using ICP-MS in the single particle mode, a significant change in the behavior of both aluminum species was detected after undergoing the artificial digestion. Nearly unchanged in the saliva, particles show dissolution and high agglomeration during the gastric state before deagglomerating again in the intestine.
Further analysis by time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed the uptake of both aluminum forms by proliferating and differentiated Caco-2 cells. For both particle forms different ions could be detected. Several aluminum-amino acid complex-derived ions from serine and valine were identified. In the case of Al2O3, Al2O2+, AlOH+, AlH2O+ and Al[(H2O)6]3+ were the main ions found co-localizing within treated cells.
Cellular effects of Al-, Ti- and Zn-containing nanomaterials on intestinal cell lines in vitro
(2016)
Aluminium-, titanium- and zinc-containing chemicals are highly abundant in food, food contact materials and consumer products. Physical and chemical conversion might lead to a certain amount of nanoscaled particles that can be taken up by the gastrointestinal tract. Nanospecific effects such as higher reactivity, increased surface or altered uptake can increase hazardous potential for human health. The aim of this study as part of the european SolNanoTOX project is to characterize toxicological effects of Al-, Zn- and Ti-containing nanomaterials on intestinal cell lines.
While toxicological potential of zinc species has been well studied, little is known about the effects of aluminium- and titanium-species. We have performed toxicological experiments on the human intestinal cell line Caco-2 for numerous endpoints: Cellular ATP and glutathione levels, apoptosis, necrosis, vesicular uptake, oxidative stress, growth rate and cell cycle modification. While zinc-containing controls showed toxic responses, our utilized aluminium- (elementary Al, γ-Al2O3) and titanium-species (TiO2, rutile) did not. Nevertheless, we detected some differences between both different aluminium nanoparticle species and aluminium ions with regard to cell viability. We also provide strong evidence for particle-specific uptake of aluminium and titanium in the intestinal cell line Caco-2.
In summary, among the different tested endpoints, Al- and Ti-containing nanomaterials did not show any toxicity in intestinal cell lines in vitro. Nevertheless, this absence of effect was not due to an absence of exposure, since particle-specific uptake was reported. Metal particle uptake over a long time might therefore be relevant for risk assessment of aluminium- and titanium-containing food products.
Although aluminium is one of the most common elements in the biosphere, little is known about its impact on human health. Since aluminium derivatives are highly abundant in food its oral uptake route is of toxicological relevance. Recently aluminium-containing nanomaterials are considered to be linked to cancer and neurodegenerative disorders. Within the frame of the european SolNanoTOX project, we therefore investigated the toxicological effects of Al-containing species in different intestinal cell lines that represent the first biological barrier for food components prior to systemic distribution.
In our in vitro digestion system, nanomaterials have been exposed to different physiological, chemical and biochemical conditions characteristic for saliva, gastric juice and the intestinal fluid. In vitro toxicity assays and cellular impedance measurements demonstrated the absence of cytotoxic effects of nanoparticles during a period of 48h after incubation. This was also observed after the digestion procedure. In contrast, aluminium ions from high concentrations of AlCl3 showed larger effects on cell viability after the digestion procedure.
In summary, the toxicological potential of aluminium-containing nanoparticles and ions to healthy intestinal cells appears to be low. Artificial digestion of these particles does not increase their toxic potential. Only for high doses of ionic aluminium, an increase of toxicity after artificial digestion was observed. Hence, we suggest that the release of Al ions from nanoparticles may lead to toxicity. Due to these observations, other cellular effects of Al-containing nanomaterials are required to be investigated.
Aluminium and its chemical derivatives are highly abundant in food, food contact materials and consumer products. Up to now little is known about its derivatization and uptake during digestion and its impact on human health. As part of the SolNanoTOX project, different aluminium species were investigated during an artificial digestion process that mimics the saliva, the stomach and the intestine regarding pH-values, duration time, chemical environment and enzymatic composition.
Two different nanomaterials (Al, Al2O3) and a soluble ionic AlCl3 control were digested and investigated by different analytical methods regarding core radius, hydrodynamic diameter, agglomeration and dissolution behavior in biological media.
The fate of nanoparticles during typical pH-values of saliva, gastric and intestinal juice was studied with dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and ICP-MS in the single particle mode. After disappearance at pH 2 the nanoparticles were detected again in the intestinal fluid, as measured by DLS. During all artificial digestion stages Al nanoparticles had a constant average SAXS radius. In contrast, the radii of Al2O3 nanoparticles changed concentration-dependently. Highest radii were observed in the stomach fluid while intestinal fluid was found to cause full recovery of the primary particles. Dissolution of digested nanoparticles in cell culture media showed a bimodal size distribution of primary particles and aggregates.
In summary, simulation of the gastrointestinal tract, mainly the change of pH settings, has provided evidence that the bioavailability of Al is likely to increase during the passage of the gut after oral uptake of aluminium-containing food products.
In the last decade the utilization of silver nanoparticles in consumer related products is enhanced. Therefore, many studies focus on investigations regarding their toxicological potential. This includes investigations concerning uptake, distribution and excretion of the particles. So far, little attention was paid to changes of physical and chemical properties in the human body. During processes like digestion, the question arises whether they can pass this barrier in a nanoscale form. In this study we analytically monitored the changes in the size distribution of colloidal silver during an artificial digestion process with the help of small angle x-ray scattering (SAXS). Therefore, we synthesized polyacrylic acid stabilized ultra-small silver nanoparticles with a radius of 3 nm and a size distribution width of 18%. The artificial digestion process mimics the gastro-intestinal passage and simulates the oral, gastric and small intestinal conditions. Additionally, food components like oil, starch, glucose and skimmed milk powder are used to provide a preferably realistic environment.
In absence of any food components the low pH initiates aggregation of the particles in the stomach. However, the particles unexpectedly stabilize in a defined cluster form with a mean radius of 12 nm. By the use of the food components oil and starch we observed that the particles are dispersed again. Now we found a bimodal size distribution of primary particles and aggregates. In contrast to that, with skimmed milk powder only a slight aggregation occurs in the stomach. In the gastric tract the particle distribution is stabilized at a mean volume weighted radius of 5 nm. Hence, skimmed milk powder acts as a colloidal stabilizer. For comparison we also used silver nitrate as a control substance. Surprisingly, we observed a formation of nanoparticles already in the saliva. During the digestion process the distribution narrows and finally in the intestine it shows a stable distribution with a mean volume weighted radius of 3 nm and a small fraction of aggregates. These results indicate that the silver nanoparticles can pass the digestion process in a nanoscale form but undergo a transformation in the size distribution. However, even from pure silver nitrate nanoparticle formation can be observed. This sketches a complex mechanism in which not only food components but also silver ions cause changes in nanoparticle size and aggregation.