The in vitro effect of hyaluronic acid on IL-1 beta production in cultured rheumatoid synovial cells

Hyaluronic acid (HA) is a multifunctional glycosaminoglycan. In this study, we examined the in vitro effect of HA on interleukin-1 beta (IL-1 beta) production in cultured rheumatoid synovial cells from 19 joints. We also examined the interactions between HA and CD44 on the cells from 11 joints by flow cytometric analysis. HA (0.3, 1 and 3 mg/ml) inhibited IL-1 beta production with phorbol 12-myristate 13-acetate (PMA) stimulation in a dose-dependent manner, and the percentage relative to the control was respectively 80 +/- 5, 66 +/- 5, and 48 +/- 3% (P < 0.05). OS/37, an anti-CD44 monoclonal antibody, is known to block the interaction between HA and CD44. Flow cytometric analysis demonstrated that OS/37 blocked fluoresceinamine-conjugated hyaluronic acid (FAHA) binding to rheumatoid arthritis synovial cells, but the percentage of inhibition varied depending on the individuals, yielding an average of inhibition as low as 22% in 11 test specimens. This result suggested that HA exhibited a binding affinity for CD44, but the binding of HA to CD44 occurred in a minor population of synovial cells. After treatment of the cells with chondroitinase, FAHA binding significantly increased (from 28% to 58%), and the blocking of FAHA binding by OS/37 was also markedly increased (from 22% to 71%). Additionally, there was a good correlation between the mean fluorescence of FITC-OS/37 staining and FAHA staining of synovial cells treated with chondroitinase, suggesting that HA binds to CD44 specifically in the major population of synovial cells treated with chondroitinase. Moreover, HA more efficiently reduced IL-1 beta production in the cells treated with chondroitinase compared with that in the non-treated cells. The results suggest the possibility that the treatment of the cells with chondroitinase modified the surface molecules including CD44 to increase their binding affinity for CD44, resulting in enhancement of HA-induced suppression of IL-1 beta production. In conclusion, HA may directly reduce IL-1 beta production by rheumatoid synovial cells and regulate it via CD44.