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.
Orally ingested nanoparticles may overcome the gastrointestinal barrier, reach the circulatory system, be distributed in the organism and cause adverse health effects. However, ingested nanoparticles have to pass through different physicochemical environments, which may alter their properties before they reach the intestinal cells. In this study, silver nanoparticles are characterised physicochemically during the course of artificial digestion to simulate the biochemical processes occurring during digestion. Their cytotoxicity on intestinal cells was investigated using the Caco-2 cell model. Using field-flow fractionation combined with dynamic light scattering and small-angle X-ray scattering, the authors found that particles only partially aggregate as a result of the digestive process. Cell viabilities were determined by means of CellTiter-Blue® assay, 4',6-diamidino-2-phenylindole-staining and real-time impedance. These measurements reveal small differences between digested and undigested particles (1–100 µg/ml or 1–69 particles/cell). The findings suggest that silver nanoparticles may indeed overcome the gastrointestinal juices in their particulate form without forming large quantities of aggregates. Consequently, the authors presume that the particles can reach the intestinal epithelial cells after ingestion with only a slight reduction in their cytotoxic potential. The study indicates that it is important to determine the impact of body fluids on the nanoparticles of interest to provide a reliable interpretation of their nano-specific cytotoxicity testing in vivo and in vitro.