Bucillamine mechanism inhibiting IL-1β-induced VEGF production from fibroblast-like synoviocytes

We investigated the bucillamine (Buc) mechanism inhibiting interleukin (IL)-1β-induced vascular endothelial growth factor (VEGF) production from human fibroblast-like synoviocytes (HFLS) which derived from the inflamed synovium of an RA patient using SA981, its active metabolite. HFLS did not produce IL-1β, spontaneously. While SA981 partially inhibited IL-1β-induced VEGF production at concentrations of 10 to 100 μM (10.1% and 14.2% inhibition of total VEGF production under IL-1β coexistence condition, respectively), it failed to inhibit IL-1β-induced IL-6 production at the same concentrations. IL-1β induced phosphorylation of the mitogen-activated protein (MAP) kinases, IκBα, c-Jun and Akt. SA981 at a concentration of 100 μM partially inhibited IL-1β-induced phosphorylation of p38MAPK and Akt (12.0% and 36.1% inhibition of each total amount of phosphoprotein under IL-1β coexistence condition, respectively). The VEGF promoter includes four transcription factors: AP1, hypoxia-inducible factor (HIF), Sp1 and AP2 binding elements. HIF-1β, Sp1 and AP1 increased under IL-1β coexistence conditions. At a concentration of 100 μM, SA981 attenuated increases in HIF-1β and Sp1 (10.1% and 19.8% inhibition of each total amount of transcription factor under IL-1β coexistence condition, respectively), but not AP1. These results suggest that SA981 partially inhibits VEGF production via modifications on IL-1β signaling. Attenuation of the expression of HIF-1β and Sp1 (but not AP1) may be a key with respect to SA981's selective inhibition of VEGF production.