Novel benzenediamine derivative FC99 ameliorates zymosan-induced arthritis by inhibiting RORγt expression and Th17 cell differentiation.

Increased IL-17-producing helper T (Th17) cells have been observed in patients with rheumatoid arthritis (RA). The retinoic-acid-related orphan nuclear receptor (RORγt) is the master regulator of Th17 cells. Our previous research showed that FC99 possesses anti-inflammation activity. However, to date the effects of FC99 on RORγt expression in Th17 cell differentiation have not been investigated yet. In the present study, we found that FC99 significantly attenuated arthritis-like symptoms, i.e., suppressing the development of paw edema in zymosan-induced arthritis (ZIA) mice. H&E staining showed that the infiltration of inflammatory cells in ankle synovial tissues was significantly suppressed. FC99 also reduced the mRNA levels of pro-inflammatory cytokines in ankle synovial tissues as shown by Q-PCR analysis. The protein levels of the pro-inflammatory cytokines in sera were also suppressed after FC99 treatment. Moreover, FC99 decreased the RORγt mRNA level in spleen tissues. Th17 cell percentage was significantly decreased in spleens and draining lymph nodes (dLNs). The mRNA and protein levels of IL-17A and IL-23 were reduced after FC99 treatment in ZIA mice. Furthermore, in vitro experiments showed that FC99 inhibited the expression of IL-6 in LPS-induced RAW264.7 cells and BMDCs. Moreover, FC99 significantly inhibited the RORγt expression in PMA-induced CD4(+) T cells and LPS-induced RAW264.7 cells. These data indicate that FC99 improves arthritis-like pathological symptoms in vivo and in vitro, which might be related to the inhibition of RORγt expression in Th17 cells. Our findings suggest that FC99 may be a potential therapeutic candidate for the treatment of RA and other inflammatory disorders.