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Chem. Res. Toxicol. 2008, 21, 1726–1732
Copper Oxide Nanoparticles Are Highly Toxic: A Comparison between Metal Oxide Nanoparticles and Carbon Nanotubes Hanna L. Karlsson, Pontus Cronholm, Johanna Gustafsson, and Lennart Mo¨ller* Unit for Analytical Toxicology, Department of Biosciences and Nutrition at NoVum, Karolinska Institutet, SE-141 57 Huddinge, Stockholm, Sweden ReceiVed February 18, 2008
Since the manufacture and use of nanoparticles are increasing, humans are more likely to be exposed occupationally or via consumer products and the environment. However, so far toxicity data for most manufactured nanoparticles are limited. The aim of this study was to investigate and compare different nanoparticles and nanotubes regarding cytotoxicity and ability to cause DNA damage and oxidative stress. The study was focused on different metal oxide particles (CuO, TiO2, ZnO, CuZnFe2O4, Fe3O4, Fe2O3), and the toxicity was compared to that of carbon nanoparticles and multiwalled carbon nanotubes (MWCNT). The human lung epithelial cell line A549 was exposed to the particles, and cytotoxicity was analyzed using trypan blue staining. DNA damage and oxidative lesions were determined using the comet assay, and intracellular production of reactive oxygen species (ROS) was measured using the oxidationsensitive fluoroprobe 2′,7′-dichlorofluorescin diacetate (DCFH-DA). The results showed that there was a high variation among different nanoparticles concerning their ability to cause toxic effects. CuO nanoparticles were most potent regarding cytotoxicity and DNA damage. The toxicity was likely not explained by Cu ions released to the cell medium. These particles also caused oxidative lesions and were the only particles that induced an almost significant increase (p ) 0.058) in intracellular ROS. ZnO showed effects on cell viability as well as DNA damage, whereas the TiO2 particles (a mix of rutile and anatase) only caused DNA damage. For iron oxide particles (Fe3O4, Fe2O3), no or low toxicity was observed, but CuZnFe2O4 particles were rather potent in inducing DNA lesions. Finally, the carbon nanotubes showed cytotoxic effects and caused DNA damage in the lowest dose tested. The effects were not explained by soluble metal impurities. In conclusion, this study highlights the in Vitro toxicity of CuO nanoparticles. Introduction Ambient airborne particles of varying size and composition are today a recognized health problem in the society. The effects associated with particles include increased rates of hospital admissions for respiratory diseases, increased use of asthma medication, and death in cancer and cardiopulmonary diseases (1). So far, mainly the health effects of particulate matter (PM1) with a diameter less than 10 and 2.5 µm (PM10 and PM2.5), respectively, have been studied. During recent years, there has been increased attention paid to the smallest particles called nanoparticles or Ultrafine particles. These particles have a diameter of less than 100 nanometer and have different properties in many aspects compared to micrometer-sized particles of the same chemical composition (2). With only a reduction in size, the properties can change dramatically regarding, e.g., electrical conductivity, magnetic characteristics, hardness, active surface area, chemical reactivity, and biological activity. These properties may be impressive from a material science perspective but may in other aspects be unwanted because of the possibility of causing toxic effects. Since the use of nanotechnology is rapidly increasing, it is critical to investigate the toxicity of different nanoparticles. At present, * To whom correspondence should be addressed. Tel: +46 8 608 91 89. Fax: + 46 8 774 68 3. E-mail:
[email protected]. 1 Abbreviations: CNT, carbon nanotubes; DCFH-DA, 2′,7′-dichlorofluorescin diacetate; FPG, formamidopyrimidine DNA glycosylase; MWCNT, multiwalled carbon nanotubes; PM, particulate matter; ROS, reactive oxygen species; SWCNT, single-walled carbon nanotubes.
the manufacture and use of nanoparticles in hundreds of commercial products is an existing scenario. To give a few examples, engineered nanoparticles are used in tires, clothes, sunscreens, cosmetics, and electronics and will be increasingly used in medicine for, e.g., imaging and drug delivery (3). For most manufactured nanoparticles, no toxicity data are available (4). Many consumer products such as sunscreens may contain nanoparticles of metal oxides (TiO2 and ZnO). Furthermore, certain occupational groups are exposed to nanoparticles of metals such as welders and workers in steel mills (5). Several studies have compared the toxicity of nanoparticles and some also with a focus on metals or metal oxides (6-13). For example, Jeng et al. showed cytotoxic effects and mitochondrial dysfunction after exposure to several metal oxide nanoparticles out of which ZnO particles were most potent (6). Similarly, another study showed highest apoptotic potency of Zn nanoparticles when compared to, e.g., Ag and Al2O3 nanoparticles (7). Hussein et al. showed toxic effects after exposure of rat liver cells to Ag nanoparticles, whereas, e.g., Fe3O4 and TiO2 nanoparticles were much less toxic (8). The ability of Cu nanoparticles to induce IL-8 production in A549 cells has also been reported (9), but when Veranth and colleagues compared several metal oxide nanoparticles and soil dust particles, regarding cytokine response in BEAS-2B cells, they found that the metal oxide particles had low potency (10). Another type of nanomaterial, which rapidly increases in production each year, is the carbon nanotubes (CNT). These new materials with unique
10.1021/tx800064j CCC: $40.75 2008 American Chemical Society Published on Web 08/19/2008
Toxicity of Nanoparticles
Chem. Res. Toxicol., Vol. 21, No. 9, 2008 1727 Table 1. Particle Characteristics.
particles CuO TiO2 ZnO CuZnFe2O4 Fe2O3 Fe3O4 carbon nanotubes
particle size in powdera [nm, average] 42 63 71 29 29 20-30
