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segunda-feira, 23 de abril de 2012

Research round-up: studies focus on nanoparticle toxicity

Danish researchers have concluded that silver nanoparticles have lethal effects on the nematode worm Caenorhabditis elegans, in research published in Ecotoxicology and Environmental Safety.
The scientists exposed the worms to two types of silver nanoparticles, and found that both substances caused adverse dose-response effects and mortality on the species, although polyvinylpyrrolidone-coated nanoparticles were more toxic that smaller uncoated particles. They also showed that pre-exposure to a low-level of nanoparticles made the nematodes more sensitive to further exposure at higher concentrations, indicating that nematodes cannot adapt to counteract nano-silver toxicity by acclimation.
Researchers have published a study demonstrating the toxic effect of different zinc oxide nanoparticles on immune cells from the lungs of mice. The scientists, from Shanghai Jiaotong University and Tianjin Polytechnic University in China, found that differences in toxicity of various zinc oxide nanoparticles is determined by nondissolved particles, which at higher concentrations cause cell death by destroying mitochondrial function and the cell membrane. The research is published in the Journal of Hazardous Materials.
Researchers from Japan have concluded that multi-walled carbon nanotubes (MWCNTs) are genotoxic to mice, in research published in Nanotoxicology. The scientists carried out both in vitro and in vivo assays to determine the effects of the nanoparticles, which they found caused genetic damage in isolated cells and dose-dependent DNA damage to the lungs of whole animals exposed by injection. The authors conclude that these effects probably occur via a mechanism involving oxidative stress and inflammatory responses.
Research examining the toxicity of different types of silver nanoparticles in the form of spheres, plates, and wires has concluded that nanoplates are considerably more toxic than other particle shapes to fish species as a result of surface defects. The scientists examined the effects of the particles in gill cells and zebrafish embryos, and demonstrated that the increased toxicity of the nanoplates could be reduced by applying a coating to smooth out the defects. They conclude this evidence demonstrates the important role of crystal defects in contributing to silver nanoparticle toxicity, in addition to the established role of the release of silver ions. They also state that the excellent correlation between the in vitro and in vivo toxicological assessment illustrates the utility of using a fish cell line in parallel with zebrafish embryos to predict environmental toxicology of nanoparticles. The research is published in ACS Nano.
Scientists studying the entry of nanoparticles into the body have published research on the interactions of nanoparticles with components of the lung using a mouse model. The scientists, from Sweden and the US, including researchers from the National Institute for Occupational Safety and Health (NIOSH), isolated inhaled single-walled carbon nanotubes from the lung fluid of mice and examined them to determine which biomolecules the particles had interacted with. They found the nanotubes had selectively adsorbed two types of the most abundant surfactant phospholipids, phosphatidylcholines and phosphatidylglycerols, to form a coating which markedly enhanced the in vitro uptake of the nanotubes by macrophage cells in the lung. The authors conclude their findings are the first demonstration of the in vivoadsorption of the surfactant lipids and proteins on single-walled carbon nanotubes in a physiologically-relevant animal model. The study is published in ACS Nano.
study on the bioavailability, toxicity and bioaccumulation of quantum dot nanoparticles made from cadmium, selenium, zinc and sulphur on invertebrate organisms has also been published. The researchers compared the effects of quantum dots to that of dissolved metal ions on the species Leptocheirus plumulosus, and found that quantum dots are accumulated to a greater extent than the dissolved ion. They also found that exposure to the nanoparticles via algae causes higher amphipod mortality, indicating that quantum dots ingested with algae are bioavailable and result in toxicity which is not observed in the absence of algae. The study is published in the journal Environmental Science and Technology.
US academics have presented an approach to correlate the results of in vitro screening assays with in vivo studies to evaluate nanoparticle toxicity, in a paper published in Toxicology. The researchers compared the effects of titanium dioxide nanoparticles on cells from the lining of the lung with the effect on rats, and found that the steepest slope of the dose-response curve can be used to correlate in vitro with in vivo results and for ranking the toxic potency of substances.