Gadolinium Compounds Signaling through TLR 4 and TLR 7 in Normal Human Macrophages: Establishment of a Proinflammatory Phenotype and Implications for the Pathogenesis of Nephrogenic Systemic Fibrosis

Abstract

Nephrogenic Systemic Fibrosis (NSF) is a progressive disorder occurring in some renal insufficiency patients exposed to Gd based contrast agents (GdBCA). Previous studies demonstrated that the GdBCA Omniscan® upregulated several innate immunity pathways in normal differentiated human macrophages, induced rapid nuclear localization of the transcription factor NFκB, and increased the expression and production of numerous profibrotic/proinflammatory cytokines, chemokines and growth factors. To further examine GdBCA stimulation of the innate immune system, cultured human embryonic kidney 293 (HEK293) cells expressing one of seven different human TLRs or one of two human Nucleotide Oligomerization Domain (NOD)-like receptors (NLRs) were exposed in vitro for 24 h to various GdBCA. The signaling activity of each compound was evaluated by its ability to activate an NFκB-inducible reporter gene. Omniscan® and gadodiamide induced strong TLR 4 and 7 mediated reporter gene activation. The other Gd compounds examined failed to induce reporter gene activation. TLR pathway inhibition using chloroquine or an inhibitor of IL-1 receptor associated kinase 1 (IRAK1) and IRAK4 in normal differentiated human macrophages abrogated Omniscan®-induced gene expression. Omniscan® and gadodiamide signaling via TLR 4 and 7 resulted in increased production and expression of numerous proinflammatory/profibrotic cytokines, chemokines, and growth factors including CXCL10, CCL2, CCL8, CXCL12, IL-4, IL-6, TGF-β and VEGF. These observations suggest that TLR activation by environmental stimuli may participate in the pathogenesis of NSF and of other fibrotic disorders including systemic sclerosis.

Induction of a type I interferon signature in normal human monocytes by gadolinium-based contrast agents: comparison of linear and macrocyclic agents

“…A second goal of the studies described was to examine the ability of the linear and macrocyclic GcBCA to affect expression levels of type I IFNs and type I IFN responsive genes, as well as genes involved in NF-κB expression and NF-κB-mediated transcriptional activation. These studies were carried out in order to provide a mechanistic link between the previously described GdBCA signalling through TLR-4 and TLR-7 [19] and the induction of the profibrotic/proinflammatory phenotype responsible for NSF development.…”

“…It seems more likely that a unique characteristic of certain linear GdBCA, or of gadodiamide in particular, such as its shape, molecular pattern or molecular surface reactivity, is responsible for the disproportionately high frequency of NSF cases associated with their use. It has been reported recently that Omniscan and gadodiamide induce TLR-4 and TLR-7-dependent expression of profibrotic/proinflammatory cytokines and growth factors in normal human differentiated macrophages [19].…”

“…These factors are secreted by activated macrophages and can then act to promote the transdifferentiation of quiescent fibroblasts to activated myofibroblasts, characterized by initiation of α-smooth muscle actin (α-SMA) expression and in dysregulated and sustained extracellular matrix production leading to tissue fibrosis. Figure modified from [19].…”

“…Recently, it has been reported that Omniscan stimulation of production of proinflammatory/profibrotic cytokines, chemokines and growth factors is mediated by Toll-like receptor (TLR)-4 and TLR-7 in normal differentiated human macrophages [19]. Numerous other studies have demonstrated that GdBCA can induce profibrotic responses in normal and NSF fibroblasts as well as in skin organ cultures [20][21][22][23].…”

Fibrosis sistémica nefrogénica: la pandemia que no fue

“…Gadodiamida podría unirse a receptores Toll-like (TLR) en monocitos o macrófagos y estimular la producción de citoquinas profibróticas y proinflamatorias 44 . Las moléculas producidas incluyen interleuquina (IL)-4, IL-6, IL-13, interferón (IFN)-γ, factor de crecimiento endotelial vascular (VEGF) y factor de crecimiento transformante beta (TGF-β), además de citoquinas dependientes del factor nuclear potenciador de las cadenas ligeras kappa de las células B activadas (NF-κB) como CCL2, CCL8, CXCL10, CXCL11 y CXCL12 44,45 . Al incubar monocitos con cloruro de gadolinio se producen citoquinas y factores de crecimiento similares, lo que orienta a que la estimulación se debe al gadolinio libre en lugar del complejo gadolinio-quelante 43 .…”