Small moleculeα-methylene-γ-butyrolactone,an evolutionarily conserved moiety in sesquiterpene lactones,ameliorates arthritic phenotype via interference DNA binding activity of NF-κB

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