Auranofin, as an anti-rheumatic gold compound, suppresses LPS-induced homodimerization of TLR4

Abstract

Toll-like receptors (TLRs), which are activated by invading microorganisms or endogenous molecules, evoke immune and inflammatory responses. TLR activation is closely linked to the development of many chronic inflammatory diseases including rheumatoid arthritis. Auranofin, an Au(I) compound, is a well-known and long-used anti-rheumatic drug. However, the mechanism as to how auranofin relieves the symptom of rheumatoid arthritis has not been fully clarified. Our results demonstrated that auranofin suppressed TLR4-mediated activation of transcription factors, NF-κB and IRF3 and expression of COX-2, a pro-inflammatory enzyme. This suppression was well correlated with the inhibitory effect of auranofin on the homodimerization of TLR4 induced by an agonist. Furthermore, auranofin inhibited NF-κ activation induced by MyD88-dependent downstream signaling components of TLR4, MyD88, IKKβ, and p65. IRF3 activation induced by MyD88-independent signaling components, TRIF and TBK1, was also downregulated by auranofin. Our results first demonstrate that auranofin suppresses the multiple steps in TLR4 signaling, especially the homodimerization of TLR4. The results suggest that the suppression of TLR4 activity by auranofin may be the molecular mechanism through which auranofin exerts anti-rheumatic activity.

Therapeutic Targeting of Toll-Like Receptors for Infectious and Inflammatory Diseases and Cancer

“…E5564 is also able to antagonize the interaction of the protein ligand EDA with TLR4 (Okamura et al, 2001), suggesting that this receptor antagonist may be useful for conditions other than sepsis and endotoxemia. Other antagonists at TLR4 include curcumin, auranofin (an antirheumatic gold compound), cinnamaldehyde, and acrolein, all of which prevent homodimerization of TLR4 (Youn et al, 2006a(Youn et al, ,b, 2008Lee et al, 2008), although how specific these agents are is uncertain. Small molecules that inhibit MyD88 binding to TLR4 are also emerging .…”

An investigation into the interactions of gold nanoparticles and anti-arthritic drugs with macrophages, and their reactivity towards thioredoxin reductase

“…This is due in part to the complexity of the autoimmune response that is at the center of RA, and the wide range of biological targets in vivo [7]. For example, auranofin inhibits activation of the transcription protein complex NF-κB [8], and reduces expression of the inflammatory enzyme COX-2 [8,9]. Production of nitric oxide [10] and the pro-inflammatory cytokines TNF-α, IL-1β and IL-6 are also reduced by auranofin treatment [9,11], while aurothiomalate also inhibits production of TNF-α [12].…”

Garlic (Allium sativum) Extract Inhibits Lipopolysaccharide-Induced Toll-Like Receptor 4 Dimerization

“…Ba/F3 cells, an IL-3-dependent murine pro-B cell line, expressing TLR4 (Flag or GFP-tagged), CD14, MD2 (Flag-tagged), and the NF-B luciferase reporter gene have been previously described. 31,32) The cells were cultured in an RPMI 1640 medium containing recombinant murine IL-3 (70 U/ml), 10% (v/v) heatinactivated fetal bovine serum (FBS), 100 units/ml of penicillin, and 100 mg/ml of streptomycin (GIBCO-BRL, Grand Island, NY, USA). RAW 264.7 cells (a murine monocytic cell line; ATCC TIB-71, Rockville, MD, USA) were cultured in Dulbecco's modified Eagle's medium (DMEM).…”

“…Protein extracts from Ba/F3 cells expressing TLR4 (Flag or GFP-tagged), CD14, MD2 (Flag-tagged), and the NF-B luciferase reporter gene for immunoprecipitation were prepared as described previously. 31,32) The samples were immunoprecipitated with the mouse-GFP antibody (Molecular Probes, Eugene, OR, USA) overnight. The solubilized immune complex was resolved by 8% SDS-PAGE and electrotransferred to a polyvinylidene difluoride membrane.…”