Nanometer-long Ge-imogolite nanotubes cause sustained lung inflammation and fibrosis in rats

Our plain-English summary of Nanometer-long Ge-imogolite nanotubes cause sustained lung inflammation and fibrosis in rats, by S. van den Brule, E. Beckers, P. Chaurand, et al (Particle and Fibre Toxicology, 2014).

The study

• Authors: S. van den Brule, E. Beckers, P. Chaurand, W. Liu, S. Ibouraadaten, M. Palmai-Pallag, F. Uwambayinema, Y. Yakoub, A. Avellan, C. Levard, V. Haufroid, E. Marbaix, A. Thill, D. Lison, J. Rose
• Journal: Particle and Fibre Toxicology
• Published: 2014;11:67
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Ge-imogolites are short aluminogermanate tubular nanomaterials with attractive prospected industrial applications. In view of their nano-scale dimensions and high aspect ratio, they should be examined for their potential to cause respiratory toxicity. Here, we evaluated the respiratory biopersistence and lung toxicity of 2 samples of nanometer-long Ge-imogolites.

Methods: Rats were intra-tracheally instilled with single wall (SW, 70 nm length) or double wall (DW, 62 nm length) Ge-imogolites (0.02-2 mg/rat), as well as with crocidolite and the hard metal particles WC-Co, as positive controls. The biopersistence of Ge-imogolites and their localization in the lung were assessed by ICP-MS, X-ray fluorescence, absorption spectroscopy and computed micro-tomography. Acute inflammation and genotoxicity (micronuclei in isolated type II pneumocytes) was assessed 3 d post-exposure; chronic inflammation and fibrosis after 2 m.

Results: Cytotoxic and inflammatory responses were shown in bronchoalveolar lavage 3 d after instillation with Ge-imogolites. Sixty days after exposure, a persistent dose-dependent inflammation was still observed. Total lung collagen, reflected by hydroxyproline lung content, was increased after SW and DW Ge-imogolites. Histology revealed lung fibre reorganization and accumulation in granulomas with epithelioid cells and foamy macrophages and thickening of the alveolar walls. Overall, the inflammatory and fibrotic responses induced by SW and DW Ge-imogolites were more severe (on a mass dose basis) than those induced by crocidolite. A persistent fraction of Ge-imogolites (15% of initial dose) was mostly detected as intact structures in rat lungs 2 m after instillation and was localized in fibrotic alveolar areas. In vivo induction of micronuclei was significantly increased 3 d after SW and DW Ge-imogolite instillation at non-inflammatory doses, indicating the contribution of primary genotoxicity.

Conclusions: We showed that nm-long Ge-imogolites persist in the lung and promote genotoxicity, sustained inflammation and fibrosis, indicating that short high aspect ratio nanomaterials should not be considered as innocuous materials. Our data also suggest that Ge-imogolite structure and external surface determine their toxic activity.

In plain English

This animal experiment tested whether very short synthetic nanotubes called Ge-imogolites harm rat lungs. Two forms were used: single-wall (about 70 nm long) and double-wall (about 62 nm long). Female Wistar rats had 0.02 to 2 mg of nanotubes placed directly into the windpipe. Comparison rats received 2 mg crocidolite asbestos, 5 mg hard metal particles (WC-Co), or saline. After a low dose, about 60% remained in the lungs at 15 days and 15% at 60 days. Three days after exposure the nanotubes caused cell damage and inflammation. At 60 days inflammation persisted, more so with the single-wall form. Lung collagen, a marker of scarring, rose with dose after both nanotube types and also rose after the single 2 mg crocidolite dose. Granulomas were seen. The authors reported that the nanotube response was more severe, on a mass dose basis, than crocidolite's. Micronuclei, a sign of genetic damage, increased in lung cells even at a dose causing no significant inflammation. The authors concluded these short nanotubes persist in the lung and promote inflammation, fibrosis and genotoxicity.

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: Animal experiment (intra-tracheal instillation in rats), with crocidolite and WC-Co as positive controls
• Who was studied: Eight to ten week old female Wistar rats, with 3 to 6 rats per group depending on the experiment; work approved by the animal research committee at the Université catholique de Louvain, Belgium; study dates not given
• Exposure: Single wall (SW, mean length 70 nm) and double wall (DW, mean length 62 nm) Ge-imogolite (aluminogermanate) nanotubes at 0.02 to 2 mg per rat, instilled in 300 μl saline. Comparison groups: 2 mg UICC crocidolite (positive control for inflammation and fibrosis), 5 mg WC-Co hard metal particles (positive control for genotoxicity), and saline (NaCl) controls.
• Main results:
  • After a non-inflammatory dose of 0.02 mg, about 60% of the initial germanium dose remained in the lungs at 15 days and 15% at 60 days. Half-lives were 21 days (SW) and 24 days (DW).
  • At 3 days, markers of cell damage (LDH) and of damage to the barrier between air spaces and blood vessels (total protein) in lung lavage fluid rose with dose compared with saline controls, except at the highest dose (2 mg). The authors noted the 2 mg suspensions were thicker.
  • At 3 days, Ge-imogolites mainly recruited macrophages and neutrophils into the air sacs, while crocidolite mainly recruited neutrophils.
  • At 60 days after 0.2 or 1 mg, total proteins and inflammatory cells in lung lavage remained elevated. The response was more severe after SW than after DW.
  • At 60 days, total lung collagen (measured as hydroxyproline) increased with dose after SW and DW Ge-imogolites (tested at 0.2 and 1 mg). Collagen also increased after crocidolite, which was tested at a single dose of 2 mg.
  • Under the microscope, lungs treated with SW and DW Ge-imogolites showed numerous granulomas. Inflammation was more diffuse with DW.
  • At 2 months, pro-inflammatory cytokines and fibrosis-related growth factors in lavage fluid were not increased after Ge-imogolites or after crocidolite (data not shown).
  • At 60 days, germanium was found mainly in scarred (fibrotic) areas of the air sacs, and X-ray analysis indicated the nanotube structure was intact.
  • The authors reported that the inflammatory and fibrotic response to Ge-imogolites was more severe, on a mass dose basis, than that to crocidolite.
  • Micronuclei (a sign of genetic damage) in isolated type II lung cells were increased 3 days after a non-inflammatory dose (0.02 mg) of SW and DW. The authors interpreted this as at least partly direct (primary) genotoxicity.
  • At 1 mg, DW further increased genotoxicity. SW at 1 mg gave a lower genotoxic response, which the authors attributed most probably to the high proportion of dead cells.
• The authors' conclusion: The authors concluded that nanometer-long Ge-imogolites persist in the deep lung and promote inflammation, fibrosis and genotoxicity. They said very short high aspect ratio nanomaterials should be assessed for respiratory hazard even when well below the 5 μm length threshold identified for fibre-induced lung toxicity.
• Limitations the authors state:
  • The thicker 2 mg suspensions may have produced a weaker response for some measures.
  • Ge-imogolites may have interfered with the cytokine assays, so IL-1β and IL-6 levels may have been underestimated, especially after DW at higher doses.

Topics

Medical terms in this study, explained in our Lexicon: Inflammation, Fibrosis, Aspect Ratio (Length-to-diameter ratio), biopersistence, Crocidolite, Genotoxicity, Micronuclei, Chronic Inflammation.

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