Shape-Related Toxicity of Titanium Dioxide Nanofibres

Our plain-English summary of Shape-Related Toxicity of Titanium Dioxide Nanofibres, by M. Allegri, M.G. Bianchi, M. Chiu, et al (PloS One, 2016).

The study

• Authors: M. Allegri, M.G. Bianchi, M. Chiu, J. Varet, A.L. Costa, S. Ortelli, M. Blosi, O. Bussolati, C.A. Poland, E. Bergamaschi
• Journal: PloS One
• Published: 2016;11(3):e0151365
• Cited by: 41 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Titanium dioxide (TiO2) nanofibres are a novel fibrous nanomaterial with increasing applications in a variety of fields. While the biological effects of TiO2 nanoparticles have been extensively studied, the toxicological characterization of TiO2 nanofibres is far from being complete. In this study, we evaluated the toxicity of commercially available anatase TiO2 nanofibres using TiO2 nanoparticles (NP) and crocidolite asbestos as non-fibrous or fibrous benchmark materials. The evaluated endpoints were cell viability, haemolysis, macrophage activation, trans-epithelial electrical resistance (an indicator of the epithelial barrier competence), ROS production and oxidative stress as well as the morphology of exposed cells. The results showed that TiO2 nanofibres caused a cell-specific, dose-dependent decrease of cell viability, with larger effects on alveolar epithelial cells than on macrophages. The observed effects were comparable to those of crocidolite, while TiO2 NP did not decrease cell viability. TiO2 nanofibres were also found endowed with a marked haemolytic activity, at levels significantly higher than those observed with TiO2 nanoparticles or crocidolite. Moreover, TiO2 nanofibres and crocidolite, but not TiO2 nanoparticles, caused a significant decrease of the trans-epithelial electrical resistance of airway cell monolayers. SEM images demonstrated that the interaction with nanofibres and crocidolite caused cell shape perturbation with the longest fibres incompletely or not phagocytosed. The expression of several pro-inflammatory markers, such as NO production and the induction of Nos2 and Ptgs2, was significantly increased by TiO2 nanofibres, as well as by TiO2 nanoparticles and crocidolite. This study indicates that TiO2 nanofibres had significant toxic effects and, for most endpoints with the exception of pro-inflammatory changes, are more bio-active than TiO2 nanoparticles, showing the relevance of shape in determining the toxicity of nanomaterials. Given that several toxic effects of TiO2 nanofibres appear comparable to those observed with crocidolite, the possibility that they exert length dependent toxicity in vivo seems worthy of further investigation.

In plain English

This laboratory study tested commercially made titanium dioxide (TiO2) nanofibres in cell cultures, comparing them with TiO2 nanoparticles and UICC crocidolite asbestos. The authors used mouse macrophage (Raw 264.7) and human A549 lung cells at 2.5 to 80 micrograms per square centimetre (40 to 80 for nanofibres on human Calu-3 airway cells), and sheep red blood cells at 1, 2 and 4 milligrams per millilitre. At the highest dose, the nanofibres lowered macrophage viability by at most 22% after 72 hours and A549 cell viability by up to 50% at 48 hours. The nanoparticles did not significantly affect viability. Crocidolite had a modest effect on macrophages comparable to the nanofibres, and it markedly lowered A549 viability. The nanofibres destroyed red blood cells (over 40% at the highest dose) significantly more than the nanoparticles or crocidolite did. Nanofibres and crocidolite, but not nanoparticles, lowered a measure of airway cell barrier integrity. Macrophages stretched along the nanofibres, and similar images were seen with crocidolite. The crocidolite sample was contaminated with bacterial endotoxin. The authors concluded that the nanofibres' toxicity in living organisms was worth investigating.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: In vitro laboratory study (cell culture and cell-free experiments) comparing TiO2 nanofibres with TiO2 nanoparticles and crocidolite asbestos as benchmark materials
• Who was studied: No people or animals were studied. The study used three cell lines: mouse peritoneal monocyte-macrophage cells (Raw 264.7), human alveolar carcinoma epithelial cells (A549) and human lung adenocarcinoma cells (Calu-3). Sheep red blood cells were used for the haemolysis test
• Exposure: Electrospun anatase TiO2 nanofibres (average length 9.9 ± 5.8 μm, average diameter 0.3 ± 0.1 μm), compared with Aeroxide P25 TiO2 nanoparticles and UICC crocidolite asbestos. Viability tests on Raw 264.7 and A549 cells used 2.5 to 80 μg/cm2. Calu-3 barrier tests used nanofibre doses of 40 to 80 μg/cm2, with nanoparticles and crocidolite at 80 μg/cm2. The red blood cell test used 1, 2 and 4 mg/mL
• Main results:
  • In macrophages, TiO2 nanofibres caused a maximal viability decrease of 22% after 72 hours at 80 μg/cm2
  • In macrophages at 80 μg/cm2, TiO2 nanoparticles did not affect viability, while crocidolite had a modest effect comparable to the nanofibres
  • In A549 alveolar epithelial cells, nanofibres caused a maximal viability decrease of 50% at 48 hours at 80 μg/cm2. Nanoparticles had no significant effect
  • Crocidolite markedly lowered A549 cell viability in a time-dependent manner
  • The red blood cell test used final concentrations of 4, 2 and 1 mg/mL of each material
  • TiO2 nanofibres were significantly more haemolytic than TiO2 nanoparticles or crocidolite, with more than 40% haemolysis at the maximal dose. Table 3 gives 42.3% for nanofibres, 10.4% for nanoparticles and 8.0% for crocidolite, all at 4 mg/mL
  • The Calu-3 barrier experiments exposed cell layers to nanofibre doses of 40 to 80 μg/cm2 for up to 12 days
  • In Calu-3 airway cell layers, nanofibres at 80 μg/cm2 lowered trans-epithelial electrical resistance (a measure of barrier integrity) by 24% after 3 days
  • The maximal decrease in trans-epithelial electrical resistance with nanofibres was 54%, at 12 days
  • Crocidolite at 80 μg/cm2 lowered trans-epithelial electrical resistance comparably to the nanofibres. TiO2 nanoparticles did not alter it
  • Nanofibres increased nitric oxide production by macrophages 5-fold at 80 μg/cm2 after 72 hours. Nanoparticles and crocidolite at 80 μg/cm2 also significantly stimulated it at 72 hours
  • Under scanning electron microscopy, macrophages exposed to nanofibres were heavily stretched along the fibres
  • Similar microscopy images were seen in macrophages exposed to crocidolite
  • In cell-free tests, nanofibres and nanoparticles produced comparable, small amounts of reactive oxygen species, while crocidolite produced very high levels
  • All materials significantly decreased glutathione, a cellular antioxidant, in macrophages
  • None of the materials significantly increased lipid peroxidation in macrophages
  • The crocidolite sample had endotoxin contamination above the assay's upper detection limit. Nanofibres and nanoparticles were below the detection limit
• The authors' conclusion: The authors concluded that, given the substantial similarity of TiO2 nanofibre and crocidolite effects in vitro, the toxicity of the nanofibres in living organisms appears worth investigating
• Limitations the authors state:
  • The authors note that the relevance of effects seen at high doses must always be critically evaluated
  • The authors did not specifically examine the mechanism behind the loss of barrier integrity
  • The authors note that the changes in macrophage shape could be due to relatively non-toxic mechanisms

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, Macrophage, Oxidative Stress.

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• Pulmonary and pleural toxicity of potassium octatitanate fibers, rutile titanium dioxide nanoparticles, and MWCNT-7 in male Fischer 344 rats — M. Abdelgied, A.M. El-Gazzar, et al. (2019)
• Exposure to nano-size titanium dioxide causes oxidative damages in human mesothelial cells: The crystal form rather than size of particle contributes to cytotoxicity — K. Hattori, K. Nakadate, et al. (2017)
• Kinetics of the bronchoalveolar leucocyte response in rats during exposure to equal airborne mass concentrations of quartz, chrysotile asbestos, or titanium dioxide — K. Donaldson, R.E. Bolton, et al. (1988)
• Safety evaluation of titanium dioxide nanoparticles by their absorption and elimination profiles — K. Sugibayashi, H. Todo, et al. (2008)

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