Thymoquinone inhibits TNF-α-induced inflammation and cell adhesion in rheumatoid arthritis synovial fibroblasts by ASK1 regulation

Tumor necrosis factor-alpha (TNF-alpha) is a pro-inflammatory cytokine produced by monocytes/macrophage that plays a pathological role in rheumatoid arthritis (RA). In this study, we investigate the effect of thymoquinone (TQ), a phytochemical found in Nigella sativa, in regulating TNF-alpha-induced RA synovial fibroblast (RA-FLS) activation. Treatment with TQ (1-5 mu M) had no marked effect on the viability of human RA-FLS. Pre-treatment of TQ inhibited TNF-alpha-induced interleukin-6 (IL-6) and IL-8 production and ICAM-1, VCAM-1, and cadherin-11 (Cad-11) expression in RA-FLS (p<0.01). Evaluation of the signaling events showed that TQ inhibited TNF-alpha-induced phospho-p38 and phospho-JNK expression, but had no inhibitory effect on NF-kappa B pathway, in RA-FLS (p <0.05; n = 4). Interestingly, we observed that selective down-regulation of TNF-alpha-induced phospho-p38 and phospho-JNK activation by TQ is elicited through inhibition of apoptosis-regulated signaling kinase 1 (ASK1). Furthermore, TNF-alpha selectively induced phosphorylation of ASK1 at Thr845 residue in RA-FLS, which was inhibited by TQ pretreatment in a dose dependent manner (p <0.01). Pre-treatment of RA-FLS with ASK1 inhibitor (TC ASK10), blocked TNF-alpha induced expression of ICAM-1, VCAM-1, and Cad-11. Our results suggest that TNF-alpha-induced ASK1-p38/NK pathway is an important mediator of cytokine synthesis and enhanced expression of adhesion molecule in RA-FLS and TQ by selectively inhibiting this pathway, may have a potential therapeutic value in regulating tissue destruction observed in RA. (C) 2015 Elsevier Inc. All rights reserved.