Thickness of multiwalled carbon nanotubes affects their lung toxicity.

Two samples of highly pure multiwalled carbon nanotubes (MWCNTs) similar in hydrophobicity and surface reactivity were prepared with similar length, <5 µm, but markedly different diameter (9.4 vs 70 nm). The samples were compared for their cytotoxic activity, uptake, and ability to induce oxidative stress (ROS production and intracellular GSH depletion) in vitro in murine alveolar macrophages (MH-S). The in vivo toxicity was evaluated by measuring biochemical (LDH activity and total proteins) and cellular responses in bronchoalveolar lavage (BAL) after intratracheal instillation in rats. Both samples were internalized in MH-S cells. However, thin MWCNTs appeared significantly more toxic than the thicker ones, both in vitro and in vivo, when compared on a mass-dose basis. The data reported herein suggest that the nanotube diameter is an important parameter to be considered in the toxicological assessment of CNTs.

Surface reactivity and cell responses to chrysotile asbestos nanofibers.

High aspect-ratio nanomaterials (HARNs) have recently attracted great attention from nanotoxicologists because of their similarity to asbestos. However, the actual risk associated with the exposure to nanosized asbestos, which escapes most regulations worldwide, is still unknown. Nanometric fibers of chrysotile asbestos have been prepared from two natural sources to investigate whether nanosize may modulate asbestos toxicity and gain insight on the hazard posed by naturally occurring asbestos, which may be defined as HARNs because of their dimensions. Power ultrasound was used to obtain nanofibers from two different chrysotile specimens, one from the dismissed asbestos mine in Balangero (Italian Western Alps) and the other from a serpentine outcrop in the Italian Central Alps. Electron microscopy, X-ray diffraction, and fluorescence spectroscopy revealed that the procedure does not affect mineralogical and chemical composition. Surface reactions related to oxidative stress, free radical generation, bioavailability of iron, and antioxidant depletion, revealed a consistent reduction in reactivity upon reduction in size. When tested on A549 human epithelial cells, the pristine but not the nanosized fibers proved cytotoxic (LDH release), induced NO production, and caused lipid peroxidation. However, nanofibers still induced some toxicity relevant oxidative stress activity (ROS production) in a dose-dependent fashion. The reduction in length and a lack of poorly coordinated bioavailable iron in nanochrysotile may explain this behavior. The present study provides a one-step procedure for the preparation of a homogeneous batch of natural asbestos nanofibers and shows how a well-known toxic material might not necessarily become more toxic than its micrometric counterpart when reduced to the nanoscale.

An integrated approach to the study of the interaction between proteins and nanoparticles.

The rapid development of nanotechnology has raised some concerns about the effects of engineered nanoparticles (NPs) on human health and the environment. At the same time, NPs have attracted intense interest because of their potential applications in biomedicine. Hence, the requirement of detailed knowledge of what takes place at the molecular level when NPs get inside living organisms is a necessary step in assessing and likely predicting the behavior of an NP. The elicited effects strongly depend on the early events occurring when NPs reach biological fluids, where the interaction with proteins is the primary process. Whereas the adsorption of proteins on biomaterials has been thoroughly investigated, the mechanisms underlying the interaction of proteins with NPs are still largely unexplored. Here we report a study of the behavior of four model proteins differing in their resistance to conformational changes, net charge, and surface charge distributions, adsorbed on two nanometric silica powders with distinct hydrophilicity. An integrated picture of the adsorption process has been obtained by applying a whole set of techniques: the extent of coverage of the silica surface and the reversibility of the process were evaluated by combining the adsorption isotherms with the changes in the zeta potential and the point of zero charge for NPs at different protein coverages; the occurrence of protein deformation was evaluated by Raman spectroscopy, and EPR spectroscopy of spin-labeled proteins provided insight into their orientation on the silica surface. We have found that the extent of coverage of the nanoparticle surface is strongly influenced by the protein structural stability as well as by the distribution of charges at the protein surface.

New detoxification processes for asbestos fibers in the environment.

Airborne asbestos fibers are associated with many serious detrimental effects on human health, while the hazard posed by waterborne fibers remains an object of debate. In adopting a precautionary principle, asbestos content in water needs to be kept as low as possible and polluting waters with asbestos should be avoided. Turci et al. (2008) recently reported a method for the decontamination of asbestos-polluted waters or landfill leachates from chrysotile that combines power ultrasound (US) with oxalic acid (Ox), an acidic chelating molecule. In the previous study, the occurrence of antigorite, a polymorph of serpentine, the mineral group encompassing chrysotile asbestos, acted as a confounding factor for complete removal of chrysotile from water. The effects of US + Ox on pure chrysotile asbestos from Val Malenco, Italian Central Alps, were examined in this investigation. In the absence of mineral contaminants, a more rapid removal of pure chrysotile from water was undertaken with respect to the previous specimen. After only 12 h of combined US + Ox acid treatment, imaging (SEM) of mineral debris indicated complete loss of fibrous habit. In addition, crystallography and vibrational features of chrysotile were not detectable (x-ray powder diffraction [XRPD] and micro-Raman spectroscopy) and elemental analysis showed a low Mg/Si ratio, i.e., the loss of the brucitic layer in chrysotile (x-ray fluorescence, XRF). Some nanometric rod-shaped debris, observed in the previous study and tentatively recognized as serpentine antigorite, was now found to be made of amorphous silica, which is relatively safe and noncarcinogenic to humans, providing further assurance regarding the safety of treated product. Thus, data indicated the proposed method was effective in detoxifying waterborne chrysotile asbestos fibers.

Low doses of pristine and oxidized single-wall carbon nanotubes affect mammalian embryonic development.

Several in vitro and in vivo studies suggest local and systemic effects following exposure to carbon nanotubes. No data are available, however, on their possible embryotoxicity in mammals. In this study, we tested the effect of pristine and oxidized single-wall carbon nanotubes (SWCNTs) on the development of the mouse embryo. To this end, SWCNTs (from 10 ng to 30 µg/mouse) were administered to female mice soon after implantation (postcoital day 5.5); 10 days later, animals were sacrificed, and uteri, placentas, and fetuses examined. A high percentage of early miscarriages and fetal malformations was observed in females exposed to oxidized SWCNTs, while lower percentages were found in animals exposed to the pristine material. The lowest effective dose was 100 ng/mouse. Extensive vascular lesions and increased production of reactive oxygen species (ROS) were detected in placentas of malformed but not of normally developed fetuses. Increased ROS levels were likewise detected in malformed fetuses. No increased ROS production or evident morphological alterations were observed in maternal tissues. No fetal and placental abnormalities were ever observed in control animals. In parallel, SWCNT embryotoxicity was evaluated using the embryonic stem cell test (EST), a validated in vitro assay developed for predicting embryotoxicity of soluble chemical compounds, but never applied in full to nanoparticles. The EST predicted the in vivo data, identifying oxidized SWCNTs as the more toxic compound.