Long, needle-like carbon nanotubes and asbestos activate the NLRP3 inflammasome through a similar mechanism

Our plain-English summary of Long, needle-like carbon nanotubes and asbestos activate the NLRP3 inflammasome through a similar mechanism, by J. Palomäki, E. Välimäki, J. Sund, et al (ACS Nano, 2011).

The study

• Authors: J. Palomäki, E. Välimäki, J. Sund, M. Vippola, P.A. Clausen, K.A. Jensen, K. Savolainen, S. Matikainen, H. Alenius
• Journal: ACS Nano
• Published: 2011;5(9):6861-70
• Cited by: 287 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Carbon nanomaterials (CNM) are targets of great interest because they have multiple applications in industry but also because of the fear of possible harmful heath effects of certain types of CNM. The high aspect ratio of carbon nanotubes (CNT), a feature they share with asbestos, is likely the key factor for reported toxicity of certain CNT. However, the mechanism to explain this toxicity is unclear. Here we investigated whether different CNM induce a pro-inflammatory response in human primary macrophages. Carbon black, short CNT, long, tangled CNT, long, needle-like CNT, and crocidolite asbestos were used to compare the effect of size and shape on the potency of the materials to induce secretion of interleukin (IL) 1-family cytokines. Our results demonstrated that long, needle-like CNT and asbestos activated secretion of IL-1β from LPS-primed macrophages but only long, needle-like CNT induced IL-1α secretion. SiRNA experiments demonstrated that the NLRP3 inflammasome was essential for long, needle-like CNT and asbestos-induced IL-1β secretion. Moreover, it was noted that CNT-induced NLRP3 inflammasome activation depended on reactive oxygen species (ROS) production, cathepsin B activity, P2X(7) receptor, and Src and Syk tyrosine kinases. These results provide new information about the mechanisms by which long, needle-like materials may cause their harmful health effects. Furthermore, the techniques used here may be of use in future risk assessments of nanomaterials.

© 2011 American Chemical Society

In plain English

This was a laboratory (in vitro) study in which human primary macrophages, derived from monocytes of healthy blood donors and differentiated for 7 days, were exposed to four carbon nanomaterials (carbon black, short multiwalled carbon nanotubes, long tangled multiwalled carbon nanotubes, long needle-like multiwalled carbon nanotubes) and to crocidolite asbestos, generally at 100 micrograms per millilitre for 6 hours. Without priming with bacterial lipopolysaccharide (LPS), none of the materials induced IL-1alpha or IL-1beta secretion. In LPS-primed macrophages, long needle-like carbon nanotubes and asbestos induced secretion of mature IL-1beta, while short or long tangled nanotubes did not do so robustly; only long needle-like nanotubes strongly induced IL-1alpha. Silencing NLRP3 with siRNA reduced IL-1beta secretion after both long needle-like nanotubes and asbestos. Inhibitors of reactive oxygen species, cathepsin B, the P2X7 receptor, and Src and Syk kinases, and P2X7 siRNA, also reduced IL-1beta. Electron microscopy was used on long needle-like nanotubes, long tangled nanotubes and asbestos, and showed all three inside macrophages. The authors concluded that long, needle-like nanotubes activate the NLRP3 inflammasome similarly to asbestos.

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 experimental study using cultured human primary macrophages exposed to carbon nanomaterials and crocidolite asbestos, with siRNA gene silencing, pharmacological inhibitors, ELISA, Western blotting and electron microscopy
• Who was studied: Human primary macrophages differentiated from peripheral blood mononuclear cells of healthy blood donors (Finnish Red Cross Blood Transfusion Service, Helsinki, Finland); each sample pooled stimulated cells from three different donors
• Exposure: Carbon black (Printex 90), short MCNT (Baytubes C 150 HP), long tangled MCNT, long needle-like MCNT (MWCNT-7) and crocidolite asbestos, mainly at 100 micrograms per millilitre for 3, 6 or 9 hours, in LPS-primed and unprimed macrophages
• Main results:
  • Without LPS priming, neither the carbon nanomaterials nor asbestos induced IL-1alpha or IL-1beta secretion from the macrophages
  • In LPS-primed macrophages, long needle-like CNT strongly induced IL-1alpha, whereas the other carbon nanomaterials and asbestos were weak inducers
  • Long needle-like CNT induced more IL-1beta secretion from LPS-primed macrophages than the other carbon nanomaterials or asbestos; mature IL-1beta was released after long needle-like CNT and asbestos but not after long tangled or short CNT
  • Secretion of IL-1alpha and IL-1beta after long needle-like CNT or asbestos peaked at 6 hours, with degradation beginning before 9 hours
  • NLRP3 siRNA reduced IL-1beta secretion after exposure to long needle-like CNT and to asbestos
  • Inhibition of reactive oxygen species (NAC, APDC, DPI) and of cathepsin B (Ca-047-Me) impaired IL-1beta secretion after long needle-like CNT and asbestos; mature cathepsin B was detected in supernatants after both
  • Pharmacological inhibition and siRNA silencing of the P2X7 receptor decreased IL-1beta secretion after long needle-like CNT and asbestos
  • The Src kinase inhibitor PP2 and the Syk kinase inhibitor SYK II dose-dependently reduced IL-1beta production induced by long needle-like CNT and asbestos
  • Transmission electron microscopy, used on long needle-like CNT, long tangled CNT and asbestos, showed these three materials inside macrophages after 6 hours at 100 micrograms per millilitre, located free in the cytosol and not in the nucleus
• The authors' conclusion: The authors concluded that long, needle-like carbon nanotubes activate inflammatory cascades by multiple mechanisms, that the effect depends on the shape of the material, and that NLRP3 inflammasome activation may be a useful screening approach supporting nanomaterial risk assessment
• Limitations the authors state:
  • The authors stated that more research is needed to confirm whether the in vitro method used is suitable for rapid risk assessment of nanomaterials
  • The authors noted that NLRP3 inflammasome activation alone is not sufficient to produce a dangerous outcome, with co-existing infection or autoimmune disorders potentially needed to increase risk

Topics

Medical terms in this study, explained in our Lexicon: Aspect Ratio (Length-to-diameter ratio), Macrophage, Crocidolite, Cytokine, Reactive Oxygen Species (ROS).

Related studies

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• PKC/ROS-Mediated NLRP3 Inflammasome Activation Is Attenuated by Leishmania Zinc-Metalloprotease during Infection — M.T. Shio, J.G. Christian, et al. (2015)
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