ABSTRACT:The interactions between nano-sized particles and living systems are commonly mediated by what adsorbs to the nanoparticle in the biological environment, its "biomolecular corona", rather than the pristine surface. Here we characterise the adhesion towards the cell membrane of nanoparticles of different material and size, and study how this is modulated by the presence or absence of a corona on the nanoparticle surface. The results are corroborated with adsorption to simple model supported lipid bilayers using a quartz crystal microbalance. We conclude that the adsorption of proteins on the nanoparticle surface strongly reduces nanoparticle adhesion in comparison to what is observed for the bare material. Nanoparticle uptake is described as a two-step process, where the nanoparticles initially adhere to the cell membrane and subsequently are internalised by the cells via energy-dependent pathways. The lowered adhesion in the presence of proteins thereby causes a concomitant decrease in nanoparticle uptake efficiency. The presence of a biomolecular corona may confer specific interactions between the nanoparticle-corona complex and the cell surface, including triggering of regulated cell uptake. An important effect of the corona is, however, a reduction in the purely unspecific interactions between the bare material and the cell membrane, which in itself disregarding specific interactions, causes a decrease in cellular uptake. We suggest that future nanoparticle-cell studies include, together with characterisation of size, charge and dispersion stability, an evaluation of the adhesion properties of the material to relevant membranes.
Cerium dioxide nanoparticles (CeO2 NPs) are increasingly being used as a catalyst in the automotive industry. Consequently, increasing amounts of CeO2 NPs are expected to enter the environment where their fate in and potential impacts are unknown. In this paper we describe the fate and effects of CeO2 NPs of three different sizes (14, 20, and 29 nm) in aquatic toxicity tests. In each standard test medium (pH 7.4) the CeO2 nanoparticles aggregated (mean aggregate size approximately 400 nm). Four test organisms covering three different trophic levels were investigated, i.e., the unicellular green alga Pseudokirchneriella subcapitata, two crustaceans: Daphnia magna and Thamnocephalus platyurus, and embryos of Danio rerio. No acute toxicity was observed for the two crustaceans and D. rerio embryos, up to test concentrations of 1000, 5000, and 200 mg/L, respectively. In contrast, significant chronic toxicity to P. subcapitata with 10% effect concentrations (EC10s) between 2.6 and 5.4 mg/L was observed. Food shortage resulted in chronic toxicity to D. magna, for wich EC10s of > or = 8.8 and < or = 20.0 mg/L were established. Chronic toxicity was found to increase with decreasing nominal particle diameter and the difference in toxicity could be explained by the difference in surface area. Using the data set, PNEC(aquatic)S > or = 0.052 and < or = 0.108 mg/L were derived. Further experiments were performed to explain the observed toxicity to the most sensitive organism, i.e., P. subcapitata. Toxicity could not be related to a direct effect of dissolved Ce or CeO2 NP uptake or adsorption, nor to an indirect effect of nutrient depletion (by sorption to NPs) or physical light restriction (through shading by the NPs). However, observed clustering of NPs around algal cells may locally cause a direct or indirect effect.
Genotoxicity of commercial colloidal and laboratory-synthesized silica nanoparticles was tested using the single cell gel electrophoresis or Comet assay. By using a carefully developed protocol and careful characterization of the nanoparticle dispersions, Comet assays were performed on 3T3-L1 fibroblasts with 3, 6, and 24 h incubations and 4 or 40 microg/ml of silica nanoparticles. No significant genotoxicity was observed for the nanoparticles tested under the conditions described, and results were independently validated in two separate laboratories, showing that in vitro toxicity testing can be quantitatively reproducible.
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