4-Octyl itaconate inhibits synovial fibroblast activation by targeting Nrf2 to exert anti-inflammatory effects in rheumatoid arthritis.

OBJECTIVES

Fibroblast-like synoviocytes (FLS) are pivotal for the expansive growth and invasiveness of rheumatoid synovitis, and patients with a fibroblastic-rich pathotype respond poorly to currently approved antirheumatic drugs. The aim of this project was to examine the anti-inflammatory effects of the nuclear factor erythroid 2-related factor 2 (Nrf2) activator 4-octyl itaconate (4-OI) on inflammatory rheumatoid arthritis (RA)-FLS-dominated pathology.

METHODS

Rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) and autologous cocultures of RA-FLS and peripheral blood mononuclear cells were cultured with 4-OI, corticosteroids or antitumor necrosis factor alpha antibodies and analysed for inflammatory activity with Western blot and enzyme-linked immunosorbent assay. 4-OI-induced transcription factor Nrf2 was genetically ablated in immortalised FLS using Clustered Regurlarly Interspaced Short Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) (CRISPR/Cas9) gene editing.In vivo, 4-OI was administered intraarticularly in the monoarticular methylated bovine serum albumin antigen-induced arthritis model and intraperitoneally in the collagen-induced arthritis, with subsequent clinical evaluation.

RESULTS

In RA-FLS in both monocultures and autolog cocultures, 4-OI treatment mediated an increase in gene expression of the Nrf2-regulated protein heme oxygenase-1 and NAD(P)H quinone dehydrogenase 1 with a concomitant decrease in monocyte chemoattractant protein-1 and specifically in monocultures also of interleukin 6 secretion. Silencing of Nrf2 reduced the effect mediated by 4-OI in RA-FLS. In the methylated bovine serum albumin mouse model, local administration of 4-OI significantly reduced joint swelling. In the collagen-induced arthritis model, a similar trend was seen accompanied by a significant reduction of interleukin 6 in serum.

CONCLUSIONS

4-OI ameliorates inflammation in models of RA, particularly in FLS-driven disease pathology. Overall, human in vitro data and murine in vivo data provide mechanistic insights into the role of 4-OI-induced activation of Nrf2 directly reducing the activation of inflammatory FLS in RA.