Background/Purpose: Nephrogenic systemic fibrosis (NSF) is a progressive iatrogenic fibrosing disorder that develops in patients with chronic kidney disease following administration of gadolinium (Gd)-based contrast agents (GBCA) for imaging studies.  In the setting of impaired renal clearance of GBCA, Gd deposits in various tissues and fibrosis develops.  However, the precise mechanism by which Gd induces systemic fibrosis is incompletely understood.  Because other profibrotic agents, such as silica and asbestos, activate the NOD-like receptor protein 3 (NLRP3) inflammasome and thereby initiate a cellular response associated with IL-1β release, we evaluated the effects of various Gd-containing compounds on inflammasome activation.

Methods: Bone marrow derived macrophages (BMDM) from wild type (WT), NLRP3^-/- and ASC^-/- mice were exposed to each of three Gd-containing compounds: GdCl₃ (free Gd salt), and Omniscan^® and Gd-diethylenetriaminepentaacetic acid (Gd-DTPA) (chelated forms of Gd).  IL-1β release into in culture media was quantified by ELISA and the extent of IL-1β processing was determined by ELISA and Western blot analysis.  Inflammasome activation and regulation was determined in macrophages polarized to an M1 or M2 phenotype using ELISA, qRT-PCR and NanoString nCounter analysis.  Finally, WT and NLRP3^-/- mice were injected intraperitoneally (i.p.) with either 500 μM Gd-DTPA or phosphate buffered saline (PBS) and recruitment of inflammatory cells to the peritoneum was analyzed by FACS.

Results: All three Gd-containing compounds induced concentration-dependent IL-1β secretion. GdCl₃ was the most potent activator, leading to the release of detectable levels of IL-1β at a concentration of 2.5 μM. Gd-DTPA and Omniscan^® also induced IL-1β production but at 200- and 4000-fold higher concentrations, respectively.  For all three substances, Western blot analysis confirmed that pro-IL-1β was processed to mature IL-1β.  None of the Gd-containing reagents induced IL-1β release by BMDM from ASC^-/- or NLRP3^-/- mice, in which inflammasome activation is impaired, demonstrating that IL-1β secretion is induced through engagement of the NLRP3 inflammasome.  Furthermore, after priming with low doses of LPS, Gd-containing compounds activated IL-4-polarized (M2) macrophages more effectively than IFNγ-polarized (M1) macrophages, since the M1 macrophages preferentially expressed genes (CD40, SOCS1, STAT1, and STAT3) known to downregulate inflammasome signaling.  Mice injected i.p. with Gd-DTPA exhibited both a relative and an absolute increase in the number of inflammatory monocytes and granulocytes recruited to the peritoneal cavity, as compared to PBS-injected mice.  This effect was markedly reduced in NLRP3^-/- mice, as compared to WT mice.

Conclusion: Both free Gd and GBCA activate the NLRP3 inflammasome in macrophages and induce IL-1β secretion in vitro and the recruitment of neutrophils and inflammatory monocytes in vivo.  The preferential activation by Gd of M2 macrophages, which promote wound healing and fibrosis, is consistent with the predominantly fibrotic presentation of NSF and may be clinically relevant.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/gadolinium-based-compounds-induce-nlrp3-dependent-il-1%ce%b2-production-and-peritoneal-inflammation/