Immunological impact of graphene oxide sheets in the abdominal cavity is governed by surface reactivity

Our plain-English summary of Immunological impact of graphene oxide sheets in the abdominal cavity is governed by surface reactivity, by A.F. Rodrigues, L. Newman, D.A. Jasim, et al (Archives of Toxicology, 2018).

The study

• Authors: A.F. Rodrigues, L. Newman, D.A. Jasim, I.A. Vacchi, C. Ménard-Moyon, L.E. Crica, A. Bianco, K. Kostarelos, C. Bussy
• Journal: Archives of Toxicology
• Published: 2018;92(11):3359-3379
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Graphene oxide (GO) is an oxidised form of graphene that has attracted commercial interest in multiple applications, including inks, printed electronics and spray coatings, which all raise health concerns due to potential creation of inhalable aerosols. Although a number of studies have discussed the toxicity of GO sheets, the in vivo impact of their lateral dimensions is still not clear. Here, we compared the effects of large GO sheets (l-GO, 1-20 µm) with those of small GO sheets (s-GO, < 1 µm) in terms of mesothelial damage and peritoneal inflammation, after intraperitoneal (i.p.) injection in mice. To benchmark the outcomes, long and rigid multi-walled carbon nanotubes (MWCNTs) that were shown to be associated with asbestos-like pathogenicity on the mesothelium were also tested. Our aim was to assess whether lateral dimensions can be a predictor of inflammogenicity for GO sheets in a similar fashion as length is for MWCNTs. While long MWCNTs dispersed in 0.5% BSA induced a granulomatous response on the diaphragmatic mesothelium and immune cell recruitment to the peritoneal cavity, GO sheets dispersed under similar conditions did not cause any response, regardless of their lateral dimensions. We further interrogated whether tuning the surface reactivity of GO by testing different dispersions (5% dextrose instead of 0.5% BSA) may change the biological outcome. Although the change of dispersion did not alter the impact of GO on the mesothelium (i.e. no granuloma), we observed that, when dispersed in protein-free 5% dextrose solution, s-GO elicited a greater recruitment of monocytic cells to the peritoneal cavity than l-GO, or when dispersed in protein-containing solution. Such recruitment coincided with the greater ability of s-GO to interact in vivo with peritoneal macrophages and was associated with a greater surface reactivity in comparison to l-GO. In conclusion, large dimension was not a determining factor of the immunological impact of GO sheets after i.p. administration. For an equal dose, GO sheets with lateral dimensions similar to the length of long MWCNTs were less pathogenic than the MWCNTs. On the other hand, surface reactivity and the ability of some smaller GO sheets to interact more readily with immune cells seem to be key parameters that can be tuned to improve the safety profile of GO. In particular, the choice of dispersion modality, which affected these two parameters, was found to be of crucial importance in the assessment of GO impact in this model. Overall, these findings are essential for a better understanding of the parameters governing GO toxicity and inflammation, and the rational design of safe GO-based formulations for various applications, including biomedicine.

In plain English

This experiment in female mice compared large graphene oxide (GO) sheets (1 to 24 µm) with small sheets (below 1 µm). Long multi-walled carbon nanotubes (MWCNTs), earlier linked to asbestos-like effects on the mesothelium, served as a comparison. No asbestos was tested. Treated mice got 50 µg in the abdominal cavity, three per group except one imaging experiment (one per material). By day 7 the nanotubes had caused granulomas (immune cell clusters) on the diaphragm lining. One day after injection they had also drawn immune cells into the cavity, including an 8.8-fold rise in monocytic cells versus solution-only controls. Neither size of GO caused granulomas. In protein solution, neither GO size significantly changed immune cell numbers. In protein-free dextrose solution, small sheets produced a 2.2-fold rise in monocytic cells over dextrose-only controls; large sheets produced no statistically significant change. The authors concluded that sheet size may not determine GO's harmfulness for the end points tested. They linked the small sheets' effect to higher surface reactivity. They noted small groups, unequal sheet numbers at equal weight doses, and that this model cannot settle lung safety.

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 (intraperitoneal injection in mice)
• Who was studied: Female C57BL/6 mice, 6 to 8 weeks old, three animals per group (one mouse per treatment for the SPECT/CT imaging experiment); UK study
• Exposure: 50 µg of large GO sheets (1 to 24 µm) or small GO sheets (below 1 µm), dispersed in 500 µL of either 0.5% bovine serum albumin solution or 5% dextrose, injected into the peritoneal cavity. Long MWCNTs, dispersed only in 0.5% BSA, served as the comparison. No asbestos fibers were tested.
• Main results:
  • MWCNTs caused distinctive granulomas on the diaphragm mesothelium by day 7
  • Neither large nor small GO sheets caused significant or visible granulomatous inflammation or fibrosis on the mesothelium at either time point (1 and 7 days)
  • One day after injection, MWCNTs in the 0.5% BSA dispersion had caused an 8.8-fold increase in monocytic cells (monocytes and macrophages) in the peritoneal cavity compared with the vehicle control (p = 0.0025)
  • Large and small GO sheets dispersed in 0.5% BSA did not cause significant immune cell recruitment to the peritoneal cavity one day after injection
  • One day after injection, small GO sheets dispersed in 5% dextrose had caused a 2.2-fold increase in monocytic cells compared with the dextrose vehicle control (p = 0.0143). This was lower than with MWCNTs (1.81 million vs 2.45 million cells per mL).
  • Large GO sheets dispersed in 5% dextrose produced no statistically significant change in the composition of immune cells in the peritoneal cavity
  • Neither GO material significantly increased LDH release (a marker of cell damage) into the peritoneal fluid
  • Imaging (one mouse per material) detected both GO materials in the bladder 4 hours after injection
  • In cells collected from the peritoneal cavity of injected mice, small GO sheets were found within the cell outlines, suggesting uptake by macrophages
  • Small GO sheets adsorbed more BSA protein than large sheets (366 mg/g vs 251 mg/g). The authors associated this with higher surface reactivity per unit surface area.
• The authors' conclusion: The authors concluded that lateral dimension may not be a determining factor of the pathogenicity of GO sheets for the end points tested in this study
• Limitations the authors state:
  • Larger groups of animals would be needed to increase statistical power
  • Dosing by mass likely meant more small sheets than large sheets were injected, so the stronger effect of small sheets might reflect particle number rather than surface reactivity
  • The lung safety of large GO sheets cannot be judged from this intraperitoneal model alone

Topics

Medical terms in this study, explained in our Lexicon: Surface Reactivity, Inflammation, Mesothelium, Peritoneal Cavity, Granuloma, Macrophage.

Related studies

• Inflammation in the pleural cavity following injection of multi-walled carbon nanotubes is dependent on their characteristics and the presence of IL-1 genes — Y.J. Arnoldussen, V. Skaug, et al. (2018)
• Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study — C.A. Poland, R. Duffin, et al. (2008)
• Length-dependent retention of carbon nanotubes in the pleural space of mice initiates sustained inflammation and progressive fibrosis on the parietal pleura — F.A. Murphy, C.A. Poland, et al. (2011)
• The Nalp3 inflammasome is essential for the development of silicosis — S.L. Cassel, S.C. Eisenbarth, et al. (2008)
• Strain differences in pleural mesothelial cell reactions induced by potassium octatitanate fibers (TISMO) infused directly into the thoracic cavity — M. Yokohira, Y. Nakano, et al. (2013)
• Length-dependent pathogenic effects of nickel nanowires in the lungs and the peritoneal cavity — C.A. Poland, F. Byrne, et al. (2012)

Browse more research in Archives of Toxicology, or return to medical research.