Gadolinium-based compounds induce NLRP3-dependent IL-1β production and peritoneal inflammation

Our plain-English summary of Gadolinium-based compounds induce NLRP3-dependent IL-1β production and peritoneal inflammation, by C. Schmidt-Lauber, L. Bossaller, H.H. Abujudeh, et al (Annals of the Rheumatic Diseases, 2015).

The study

• Authors: C. Schmidt-Lauber, L. Bossaller, H.H. Abujudeh, G.I. Vladimer, A. Christ, K.A. Fitzgerald, E. Latz, E.M. Gravallese, A. Marshak-Rothstein, J. Kay
• Journal: Annals of the Rheumatic Diseases
• Published: 2015;74(11):2062-9
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: Nephrogenic systemic fibrosis (NSF) is a progressive fibrosing disorder that may develop in patients with chronic kidney disease after administration of gadolinium (Gd)-based contrast agents (GBCAs). In the setting of impaired renal clearance of GBCAs, Gd deposits in various tissues and fibrosis subsequently develops. However, the precise mechanism by which fibrosis occurs in NSF is incompletely understood. Because other profibrotic agents, such as silica or asbestos, activate the nucleotide-binding oligomerisation domain (NOD)-like receptor protein 3 (NLRP3) inflammasome and initiate interleukin (IL)-1β release with the subsequent development of fibrosis, we evaluated the effects of GBCAs on inflammasome activation.

Methods: Bone marrow derived macrophages from C57BL/6, Nlrp3(-/-) and Asc(-/-) mice were incubated with three Gd-containing compounds and IL-1β activation and secretion was detected by ELISA and western blot analysis. Inflammasome activation and regulation was investigated in IL-4- and interferon (IFN)γ-polarised macrophages by ELISA, quantitative real time (qRT)-PCR and NanoString nCounter analysis. Furthermore, C57BL/6 and Nlrp3(-/-)mice were intraperitoneally injected with GBCA and recruitment of inflammatory cells to the peritoneum was analysed by fluorescence-activated cell sorting (FACS).

Results: Free Gd and GBCAs activate the NLRP3 inflammasome and induce IL-1β secretion in vitro. Gd-diethylenetriaminepentaacetic acid also induces the recruitment of neutrophils and inflammatory monocytes to the peritoneum in vivo. Gd activated IL-4-polarised macrophages more effectively than IFNγ-polarised macrophages, which preferentially expressed genes known to downregulate inflammasome activity.

Conclusions: These data suggest that Gd released from GBCAs triggers a NLRP3 inflammasome-dependent inflammatory response that leads to fibrosis in an appropriate clinical setting. The preferential activation of IL-4-differentiated macrophages is consistent with the predominantly fibrotic presentation of NSF.

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In plain English

This mouse laboratory study examined gadolinium, a metal in MRI contrast agents. Gadolinium has been linked to nephrogenic systemic fibrosis, a scarring disease, in people with kidney disease. Asbestos was not tested; the authors cited it, with silica, only as an agent known to trigger an immune sensor, the NLRP3 inflammasome. Mouse immune cells (macrophages), first primed with lipopolysaccharide (LPS), released the inflammatory signal IL-1β when exposed to three gadolinium compounds. Free gadolinium chloride was strongest, producing 1085 plus or minus 576 pg/mL at 2.5 μM, without signs of increased cell death. Cells lacking NLRP3 or its partner protein ASC did not respond. Among LPS-primed macrophages pushed toward 'M2' (linked to healing and scarring) or 'M1' types, M2-type cells released more IL-1β. In live mice, a gadolinium compound injected into the abdominal cavity increased inflammatory cells there after 24 hours; this influx was markedly reduced in mice lacking NLRP3. The authors concluded that the data suggest gadolinium released from contrast agents triggers an NLRP3-dependent inflammatory response that leads to fibrosis in an appropriate clinical setting.

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: Laboratory experiments on mouse bone marrow macrophages in culture, plus an animal experiment in live mice
• Who was studied: Macrophages grown from the bone marrow of normal (C57BL/6) mice and of mice lacking the NLRP3 or ASC genes. For the live-animal experiment: male mice aged 9 to 10 weeks, normal mice (n=8) and NLRP3-lacking mice (n=7), pooled from three experiments. The work was done at the University of Massachusetts; dates are not given.
• Exposure: Macrophages were first primed with lipopolysaccharide (LPS), then exposed to three gadolinium compounds: gadolinium chloride (free, unchelated gadolinium), Omniscan (gadodiamide contrast agent), and Gd-DTPA. Nigericin, poly(dA:dT) and silica were used as comparison stimulants. No asbestos was tested.
• Main results:
  • In LPS-primed macrophages from normal mice, all three gadolinium compounds caused IL-1β release. Free gadolinium chloride was the most potent, giving 1085 plus or minus 576 pg/mL at 2.5 μM. Gd-DTPA needed 500 μM and Omniscan 10 mM to induce IL-1β.
  • None of the gadolinium compounds produced evidence of increased cell death in the macrophages.
  • Macrophages lacking ASC or NLRP3 did not release IL-1β in response to any of the gadolinium compounds.
  • Among LPS-primed macrophages, unpolarised and M2-type (IL-4-polarised) cells released more IL-1β in response to each gadolinium compound than M1-type (IFNγ-polarised) cells. In the M1-type cells the response was barely detectable.
  • LPS-primed M2-type cells expressed about three times as much IL-1β as LPS-primed M1-type cells. STAT1 and STAT3, which are known to dampen inflammasome signalling, were expressed at much higher levels in the M1-type cells.
  • In normal mice, Gd-DTPA injected into the abdominal cavity increased the relative and absolute numbers of inflammatory monocytes and granulocytes there after 24 hours, compared with mice injected with saline (PBS).
  • This influx of inflammatory cells was markedly reduced in NLRP3-lacking mice compared with Gd-DTPA-injected normal mice.
• The authors' conclusion: The authors concluded that the data suggest gadolinium released from gadolinium-based contrast agents triggers an NLRP3 inflammasome-dependent inflammatory response that leads to fibrosis in an appropriate clinical setting. They added that the stronger activation of M2-type macrophages is consistent with the mainly fibrotic presentation of nephrogenic systemic fibrosis.
• Limitations the authors state:
  • The authors stated that further studies are needed to clarify the roles of NLRP3 inflammasome activation and M2 macrophage polarisation in nephrogenic systemic fibrosis.
  • The authors noted that it remains to be determined whether the gene expression differences between primed M1-type and M2-type macrophages also hold in living animals.
  • The authors noted that dividing macrophages into M1 and M2 types appears to oversimplify their diversity.

Topics

Medical terms in this study, explained in our Lexicon: Inflammation, Fibrosis, Macrophage, Peritoneum.

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