Nathalie Herlin-Boime

Titanium dioxide nanoparticles exhibit genotoxicity and impair DNA repair activity in A549 cells

Abstract Titanium dioxide nanoparticles (TiO2-NPs) are produced in large quantities, raising concerns about their impact for human health. The aim of this study was to deeply characterize TiO2-NPs genotoxic potential to lung cells, and to link genotoxicity to physicochemical characteristics, e.g., size, specific surface area, crystalline phase. A549 cells were exposed to a panel of TiO2-NPs with diameters ranging from 12 to 140 nm, either anatase or rutile. A set of complementary techniques (comet and micronucleus assays, gamma-H2AX immunostaining, 8-oxoGuanine analysis, H2-DCFDA, glutathione content, antioxidant enzymes activities) allowed us to demonstrate that small and spherical TiO2-NPs, both anatase and rutile, induce single-strand breaks and oxidative lesions to DNA, together with a general oxidative stress. Additionally we show that these NPs impair cell ability to repair DNA, by inactivation of both NER and BER pathways. This study thus confirms the genotoxic potential of TiO2-NPs, which may preclude their mutagenicity and carcinogenicity.

Size-, Composition- and Shape-Dependent Toxicological Impact of Metal Oxide Nanoparticles and Carbon Nanotubes toward Bacteria

Ecotoxicological effects of nanoparticles (NP) are still poorly documented while their commercialization for industrial and household applications increases. The aim of this study was to evaluate the influence of physicochemical characteristics on metal oxide NP and carbon nanotubes toxicological effects toward bacteria. Two strains of bacteria, Cupriavidus metallidurans CH34 and Escherichia coli MG1655 were exposed to TiO(2) or Al(2)O(3) NP or to multiwalled-carbon nanotubes (MWCNT). Particular attention was paid on optimizing NP dispersion to obtain nonagglomerated suspensions. Our results show that NP toxicity depends on their chemical composition, size, surface charge, and shape but not on their crystalline phase. MWCNT toxicity does not depend on their purity. Toxicity also depends on the bacterial strain: E. coli MG1655 is sensitive to NP, whereas C. metallidurans CH34 is not. Interestingly, NP are accumulated in both bacterial strains, and association between NP and bacteria is necessary for bacterial death to occur. NP may then represent a danger for the environment, causing the disappearance of some sensitive bacterial strains such as E. coli MG1655, but also being mobilized by nonsensitive strains such as C. metallidurans CH34 and transported through the whole ecosystem.

In vitro investigation of oxide nanoparticle and carbon nanotube toxicity and intracellular accumulation in A549 human pneumocytes

If released in the environment, nanomaterials might be inhaled by populations and cause damage to the deepest regions of the respiratory tract, i.e., the alveolar compartment. To model this situation, we studied the response of A549 human pneumocytes after exposure to aluminium oxide or titanium oxide nanoparticles, and to multi-walled carbon nanotubes. The influence of size, crystalline structure and chemical composition was investigated. After a detailed identification of nanomaterial physico-chemical characteristics, cells were exposed in vitro and viability and intracellular accumulation were assessed. In our conditions, carbon nanotubes were more toxic than metal oxide nanoparticles. Our results confirmed that both nanotubes and nanoparticles are able to rapidly enter into cells, and distribute in the cytoplasm and intracellular vesicles. Among nanoparticles, we demonstrate significant difference in biological response as a function of size, crystalline phase and chemical composition. Their toxicity was globally lower than nanotubes toxicity. Among nanotubes, the length did not influence cytotoxicity, neither the presence of metal catalyst impurities.

Accumulation, translocation and impact of TiO2 nanoparticles in wheat (Triticum aestivum spp.): Influence of diameter and crystal phase

Intensive production of TiO(2) nanoparticles (TiO(2)-NPs) would lead to their release in the environment. Their ecotoxicological impact is still poorly documented, while their use in commercial goods is constantly increasing. In this study we compare root accumulation and root-to-shoot translocation in wheat of anatase and rutile TiO(2)-NPs with diameters ranging from 14 nm to 655 nm, prepared in water. NP distribution in plant tissues was mapped by synchrotron-radiation micro-X-ray fluorescence, observed by transmission electron microscopy and quantified in the different compartments of plant roots by micro-particle-induced X-ray emission. Our results provide evidence that the smallest TiO(2)-NPs accumulate in roots and distribute through whole plant tissues without dissolution or crystal phase modification. We suggest a threshold diameter, 140 nm, above which NPs are no longer accumulated in wheat roots, as well as a threshold diameter, 36 nm, above which NPs are accumulated in wheat root parenchyma but do not reach the stele and consequently do not translocate to the shoot. This accumulation does not impact wheat seed germination, biomass and transpiration. It does not induce any modification of photosynthesis nor induce oxidative stress. However exposure of wheat plantlets to the smallest NPs during the first stages of development causes an increase of root elongation. Collectively, these data suggest that only the smallest TiO(2)-NPs may be accumulated in wheat plants, although in limited amounts and that their impact is moderate.

Carbon nanoparticles from laser pyrolysis

Carbon nanoparticles synthesised by laser pyrolysis of hydrocarbons in a flow reactor have been investigated as a function of laser power. Samples are cross-characterised by high resolution transmission electron microscopy (HRTEM) and infrared (IR) spectroscopy. Nanoparticles appear highly aromatic in character in all the experimental conditions explored here. As the flame temperature in the interaction zone increases, the nanoparticles evolve drastically from poorly organised, highly hydrogenated samples toward turbostratic concentric particles of carbon. The multiscale organisation of the samples and its evolution with the synthesis parameters are quantitatively determined and correlated to IR properties through an original development of HRTEM image analysis. The multiscale organisation does not reduce to the classical view of assemblies of basic structural units (BSU) of aromatic bricks. More refined models are proposed where non-stacked aromatic layers play a noticeable role and lead to a better understanding of the samples optical properties. Possible contribution to a better understanding of carbon cosmic dust is discussed from an astrophysical point of view.

Titanium dioxide nanoparticle impact and translocation through ex vivo, in vivo and in vitro gut epithelia

BackgroundTiO2 particles are commonly used as dietary supplements and may contain up to 36% of nano-sized particles (TiO2-NPs). Still impact and translocation of NPs through the gut epithelium is poorly documented.ResultsWe show that, in vivo and ex vivo, agglomerates of TiO2-NPs cross both the regular ileum epithelium and the follicle-associated epithelium (FAE) and alter the paracellular permeability of the ileum and colon epithelia. In vitro, they accumulate in M-cells and mucus-secreting cells, much less in enterocytes. They do not cause overt cytotoxicity or apoptosis. They translocate through a model of FAE only, but induce tight junctions remodeling in the regular ileum epithelium, which is a sign of integrity alteration and suggests paracellular passage of NPs. Finally we prove that TiO2-NPs do not dissolve when sequestered up to 24 h in gut cells.ConclusionsTaken together these data prove that TiO2-NPs would possibly translocate through both the regular epithelium lining the ileum and through Peyer’s patches, would induce epithelium impairment, and would persist in gut cells where they would possibly induce chronic damage.

In vitro evaluation of SiC nanoparticles impact on A549 pulmonary cells: Cyto-, genotoxicity and oxidative stress

Silicon carbide (SiC) is considered a highly biocompatible material, consequently SiC nanoparticles (NPs) have been proposed for potential applications in diverse areas of technology. Since no toxicological data are available for these NPs, the aim of this study was to draw their global toxicological profile on A549 lung epithelial cells, using a battery of classical in vitro assays. Five SiC-NPs, with varying diameters and Si/C ratios were used, and we show that these SiC-NPs are internalized in cells where they cause a significant, though limited, cytotoxic effect. Cell redox status is deeply disturbed: SiC-NP exposure cause reactive oxygen species production, glutathione depletion and inactivation of some antioxidant enzymes: glutathione reductase, superoxide dismutase, but not catalase. Finally, the alkaline comet assay shows that SiC-NPs are genotoxic. Taken together, these data prove that SiC-NPs biocompatibility should be revisited.

Comparative uptake and impact of TiO₂ nanoparticles in wheat and rapeseed.

Up to 2 million tons per year of titanium dioxide (TiO2) nanoparticles (NP) are produced worldwide. This extensive production is postulated to result in release into the environment with subsequent contamination of soils and plants; however, few studies have examined TiO2-NP uptake and impact on plants. In this study, wheat and rapeseed plantlets were exposed to 14 nm or 25 nm anatase TiO2-NP in hydroponics conditions, either through root or leaf exposure. Microparticle-induced x-ray emission (μPIXE) coupled with Rutherford backscattering spectroscopy (RBS) was used to quantify absorbed titanium (Ti). Micro x-ray fluorescence (μXRF) based on synchrotron radiation was used to evaluate Ti distribution in roots and leaves. Our results show that both TiO2-NP are accumulated in these plantlets upon root exposure and that Ti content is higher in rapeseed than wheat. Ti distribution in root cross sections depended on NP agglomeration state. NP are also accumulated in plantlets upon leaf exposure. Finally, it was found that TiO2-NP exposure induced increased root elongation but did not affect germination, evapotranspiration, and plant biomass. Taken together, these results confirm that TiO2-NP may be accumulated in plant crops but may only moderately impact plant development.

Photoluminescence decay dynamics of noninteracting silicon nanocrystals

Time-resolved photoluminescencemeasurements on size-selected siliconnanocrystals have been carried out in order to elucidate the nonexponential behavior of the photoluminescence decay kinetics. The nanoparticles are gas-phase synthesized, extracted as a supersonic beam, size selected, and deposited downstream as films of variable densities. The nanoparticlenumber densities were determined by atomic force microscopy. The photoluminescence properties appear totally independent of the film density. Even in the very low density film where nanoparticles are completely isolated from each other, the decay kinetics corresponds to a stretched exponential law. This means that the stretched exponential kinetics does not originate from the interaction between nanoparticles, but is actually a characteristic of the siliconnanocrystals.

Investigation of titanium dioxide nanoparticles toxicity and uptake by plants

Nanoparticles (NP) are introduced in a growing number of commercial products and their production may lead to their release in the environment. Plants may be a potential entry point for NP in the food chain. Up to now, results describing NP phytotoxical effects and plant accumulation are scarce and contradictory. To increase knowledge on titanium dioxide NP (TiO2-NPs) accumulation and impact on plants, we designed a study on three plant species, namely wheat (Triticum aestivum), oilseed rape (Brassica napus) and Arabidopsis thaliana. These plants were exposed in hydroponics to a panel of well-characterized TiO2-NPs, with diameters ranging from 12 to 140 nm, either anatase or rutile. Their accumulation in plant tissues is currently being assessed by complementary imaging techniques: scanning electron microscopy (SEM), transmission electron microscopy (TEM), micro-X-ray fluorescence (SR-μ-XRF) imaging and micro-particle induced X-ray emission (μ-PIXE) imaging. Moreover, the impact of TiO2-NP exposure on germination rate, root elongation, dry biomass and evapotranspiration is evaluated. Preliminary results are presented here, with data collected on wheat plants exposed to 12 nm and 25 nm anatase TiO2-NPs. These results show that TiO2-NPs are taken up by plants, and do not significantly alter their germination and root elongation. These results underline the necessity of deeper evaluation of nanoparticle ecotoxicity, and particularly on their interaction with plants.