http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.files/fileID/14490

Correlating Nanoscale Titania Structure with Toxicity: A Cytotoxicity and Inflammatory Response Study with Human Dermal Fibroblasts and Human Lung Epithelial Cells

Ultrafine (nanometre) particle mediated lung injury

Titanium dioxide (TiO2) nanoparticles are manufactured worldwide in large quantities for use in a wide range of applications including pigment and cosmetic manufacturing. Although TiO2 is chemically inert, TiO2 nanoparticles can cause negative health effects, such as respiratory tract cancer in rats. However, the mechanisms involved in TiO2-induced genotoxicity and carcinogenicity have not been clearly defined and are poorly studied in vivo. The present study investigates TiO2 nanoparticles–induced genotoxicity, oxidative DNA damage, and inflammation in a mice model. We treated wild-type mice with TiO2 nanoparticles in drinking water and determined the extent of DNA damage using the comet assay, the micronuclei assay, and the γ-H2AX immunostaining assay and by measuring 8-hydroxy-2′-deoxyguanosine levels and, as a genetic instability endpoint, DNA deletions. We also determined mRNA levels of inflammatory cytokines in the peripheral blood. Our results show that TiO2 nanoparticles induced 8-hydroxy-2′-deoxyguanosine, γ-H2AX foci, micronuclei, and DNA deletions. The formation of γ-H2AX foci, indicative of DNA double-strand breaks, was the most sensitive parameter. Inflammation was also present as characterized by a moderate inflammatory response. Together, these results describe the first comprehensive study of TiO2 nanoparticles–induced genotoxicity in vivo in mice possibly caused by a secondary genotoxic mechanism associated with inflammation and/or oxidative stress. Given the growing use of TiO2 nanoparticles, these findings raise concern about potential health hazards associated with TiO2 nanoparticles exposure. [Cancer Res

https://cancerres.aacrjournals.org/content/canres/69/22/8784.full.pdf

Titanium dioxide nanoparticles induce DNA damage and genetic instability in vivo in mice.

Ambient fine particles consist of ultrafine particles (< 100 nm) and accumulation-mode particles (approximately 100 to 1,000 nm). Our hypothesis that ultrafine particles can have adverse effects in humans is based on results of our earlier studies with particles of both sizes and on the finding that urban ultrafine particles can reach mass concentrations of 40 to 50 micrograms/m3, equivalent to number concentrations of 3 to 4 x 10(5) particles/cm3. The objectives of the exploratory studies reported here were to (1) evaluate pulmonary effects induced in rats and mice by ultrafine particles of known high toxicity (although not occurring in the ambient atmosphere) in order to obtain information on principles of ultrafine particle toxicology; (2) characterize the generation and coagulation behavior of ultrafine particles that are relevant for urban air; (3) study the influence of animals' age and disease status; and (4) evaluate copollutants as modifying factors. We used ultrafine Teflon (polytetrafluoroethylene [PTFE]*) fumes (count median diameter [CMD] approximately 18 nm) generated by heating Teflon in a tube furnace to 486 degrees C to evaluate principles of ultrafine particle toxicity that might be helpful in understanding potential effects of ambient ultrafine particles. Teflon fumes at ultrafine particle concentrations of approximately 50 micrograms/m3 are extremely toxic to rats when inhaled for only 15 minutes. We found that neither the ultrafine Teflon particles alone when generated in argon nor the Teflon fume gas-phase constituents when generated in air were toxic after 25 minutes of exposure. Only the combination of both phases when generated in air caused high toxicity, suggesting the existence of either radicals on the particle surface or a carrier mechanism of the ultrafine particles for adsorbed gas-phase compounds. We also found rapid translocation of the ultrafine Teflon particles across the epithelium after their deposition, which appears to be an important difference from the behavior of larger particles. Furthermore, the pulmonary toxicity of the ultrafine Teflon fumes could be prevented by adapting the animals with short 5-minute exposures on 3 days prior to a 15-minute exposure. This shows the importance of preexposure history in susceptibility to acute effects of ultrafine particles. Aging of the fresh Teflon fumes for 3.5 minutes led to a predicted coagulation resulting in particles greater than 100 nm that no longer caused toxicity in exposed animals. This result is consistent with greater toxicity of ultrafine particles compared with accumulation-mode particles. When establishing dose-response relationships for intratracheally instilled titanium dioxide (TiO2) particles of the size of the urban ultrafine particles (20 nm) and of the urban accumulation-mode particles (250 nm), we observed significantly greater pulmonary inflammatory response to ultrafine TiO2 in rats and mice. The greater toxicity of the ultrafine TiO2 particles correlated well with their greater surface area per mass. Ultrafine particles of carbon, platinum, iron, iron oxide, vanadium, and vanadium oxide were generated by electric spark discharge and characterized to obtain particles of environmental relevance for study. The CMD of the ultrafine carbon particles was approximately 26 nm, and that of the metal particles was 15 to 20 nm, with geometric standard deviations (GSDs) of 1.4 to 1.7. For ultrafine carbon particles, approximately 100 micrograms/m3 is equivalent to 12 x 10(6) particles/cm3. Homogeneous coagulation of these ultrafine particles in an animal exposure chamber occurred rapidly at 1 x 10(7) particles/cm3, so that particles quickly grew to sizes greater than 100 nm. Thus, controlled aging of ultrafine carbon particles allowed the generation of accumulation-mode carbon particles (due to coagulation growth) for use in comparative toxicity studies. We also developed a technique to generate ultrafine particles consisting of the stable isotope 13C by using 13C-graphite electrodes made in our laboratory from amorphous 13C powder. These particles are particularly useful tools for determining deposition efficiencies of ultrafine carbon particles in the respiratory tracts of laboratory animals and the translocation of particles to extrapulmonary sites. For compromised animals, we used acute and chronic pulmonary emphysema; a low-dose endotoxin inhalation aimed at priming target cells in the lung was also developed. Other modifying factors were age and copollutant (ozone) exposure. Exposure concentrations of the generated ultrafine particles for acute rodent inhalation studies were selected on the basis of lung doses predicted to occur in people inhaling approximately 50 micrograms/m3 urban ultrafine particles. Concentrations that achieved the same predicted lung burden per unit alveolar surface were used in rodents. (ABSTRACT TRUNCATED)

Acute pulmonary effects of ultrafine particles in rats and mice.

https://www.rachel.org/files/document/Impairment_of_Alveolar_Macrophage_Phagocytosis.pdf

Impairment of alveolar macrophage phagocytosis by ultrafine particles.

Epidemiological evidence has been accumulating showing a strong relationship between particulate environmental air pollution (PM10) and end-points of respiratory ill health such as attacks of asthma, COPD, diminished lung function and cardio-vascular deaths (Pope et al., 1995). To date there has been no plausible biological hypothesis to explain this relationship at the very low airborne mass concentrations of particulate air pollution that are found (< 50 \ig ml"). We recently hypothesised (Seaton et al., 1995) that an ultrafine (< 100 nm diameter) component of PM10 is responsible for its adverse effects. This is based on the initial studies of Oberdorster and colleagues (Feirin et al., 1992) who demonstrated that titanium dioxide in the ultrafine form (20 nm diameter) was highly inflammogenic to the lungs of rats compared to fine (200 nm diameter) TiO2 particles at the same airborne mass concentration. We now hypothesise that the adverse effects of PM10 on the lung result from free radical activity at the surface of an ultrafine fraction. We further hypothesise that the interstitialisation that was seen with UFTiO2 (Ferin et al., 1992) could similarly occur with the ultrafine component of PM10. If the ultrafine material has free radical activity then the increased surface area that is presented to the epithelial surface by a relatively small mass of ultrafine particles could compromise epithelial integrity leading to interstitialisation. We demonstrate here that ultrafine TiO2 and PM10 both have hydroxyl radical activity and that UFTiO2 is capable of causing hydroxyl radical-mediated membrane damage to erythrocytes; fine TiO2 has much less of these properties. Additionally PM10 hydroxyl radical activity is either in the ultrafine fraction or is released in soluble form.

E. Benton

Papers

Surface Free Radical Activity of PM10 and Ultrafine Titanium Dioxide: A Unifying Factor in Their Toxicity?