Small molecule -methylene--butyrolactone, an evolutionarily conserved moiety in sesquiterpene lactones, ameliorates arthritic phenotype interference DNA binding activity of NF-B.

Rheumatoid arthritis (RA) is an inflammatory disease accompanied by abnormal synovial microenvironment (SM). Sesquiterpene lactones (SLs) are the main anti-inflammatory ingredients of many traditional herbs utilized in RA treatment. -Methylene--butyrolactone (-M--B) is a core moiety that widely exists in natural SLs. This study was designed to investigate the anti-arthritic potential of -M--B as an independent small molecule and . -M--B exhibited stronger electrophilicity and anti-inflammatory effects than the other six analogs. -M--B inhibited the production of pro-inflammatory mediators repolarizing M1 macrophages into M2 macrophages. The transcriptome sequencing suggested that -M--B regulated the immune system pathway. Consistently, -M--B attenuated collagen type II-induced arthritic (CIA) phenotype, restored the balance of Tregs-macrophages and remodeled SM repolarizing the synovial-associated macrophages in CIA mice. Mechanistically, although -M--B did not prevent the trans-nucleus of NF-B it interfered with the DNA binding activity of NF-B direct interaction with the sulfhydryl in cysteine residue of NF-B p65, which blocked the activation of NF-B. Inhibition of NF-B reduced the M1 polarization of macrophage and suppressed the synovial hyperplasia and angiogenesis. -M--B failed to ameliorate CIA in the presence of -acetylcysteine or when the mice were subjected to the macrophage-specific deficiency of . In conclusion, -M--B significantly attenuated the CIA phenotype by directly targeting NF-B p65 and inhibiting its DNA binding ability. These results suggest that -M--B has the potential to serve as an alternative candidate for treating RA. The greater electrophilicity of -M--B, the basis for triggering strong anti-inflammatory activity, accounts for the reason why -M--B is evolutionarily conserved in the SLs by medical plants.