Anti–interleukin‐6 receptor antibody therapy reduces vascular endothelial growth factor production in rheumatoid arthritis

Abstract

Objective: To investigate whether interleukin‐6 (IL‐6) is a regulator of vascular endothelial growth factor (VEGF) in rheumatoid arthritis (RA). Methods: Serum VEGF levels in RA patients were assayed before and after 8 weeks or 24 weeks of maintenance therapy with humanized anti–IL‐6 receptor monoclonal antibody (anti–IL‐6R mAb). VEGF secreted by RA synovial fibroblasts cultured in the presence of IL‐6, IL‐1β, and/or tumor necrosis factor α (TNFα) was measured. The inhibitory effect of anti–IL‐6R mAb, recombinant IL‐1 receptor antagonist (IL‐1Ra), and anti‐TNFα mAb on VEGF production was also examined. Results: Serum VEGF levels in RA patients before anti–IL‐6R mAb therapy were significantly higher than those in healthy controls (P < 0.0005). Treatment of RA patients with anti–IL‐6R mAb normalized serum VEGF levels. In the in vitro study, IL‐6 and IL‐1β each induced a slight amount of VEGF production in synovial cells, but TNFα did not. Although VEGF‐inducing activity of these cytokines was not remarkable when they were added alone, IL‐6 acted synergistically with IL‐1β or TNFα to induce VEGF production. There was no synergistic effect between IL‐1β and TNFα. In the presence of all of these cytokines, anti–IL‐6R mAb eliminated the synergistic effect of IL‐6, IL‐1β, and TNFα, while IL‐1Ra or anti‐TNFα mAb did not. Conclusion: Anti–IL‐6R mAb therapy reduced VEGF production in RA. IL‐6 is the pivotal cytokine that induces VEGF production in synergy with IL‐1β or TNFα, and this may be the mechanism by which IL‐6 blockade effectively suppresses VEGF production in synovial fibroblasts.