Anti-interleukin-1 and anti-CD44 interventions producing significant inhibition of cartilage destruction in an in vitro model of cartilage invasion by rheumatoid arthritis synovial fibroblasts

Abstract

Objective To establish an in vitro model for the investigation of destructive processes in rheumatoid arthritis (RA), to study the interaction between fibroblasts, macrophages, and chondrocytes, and to evaluate strategies to inhibit joint destruction in RA. Methods Human and bovine chondrocytes cultured in sponges pretreated with native bovine embryonic extracellular matrix produced a cartilaginous matrix reflected by the incorporation of ³⁵S into proteoglycans. The 3‐dimensional culture system was optimized for the number of chondrocytes (10⁵ cells/sponge), the timing of ³⁵S incorporation (day 21 after chondrocyte isolation), and the medium (20% fetal calf serum). RA synovial fibroblasts (RASF; 10⁵) were added, and the matrix destruction mediated by these RASF was monitored by the release of ³⁵S. The system was modulated by the addition of monocytes (U937 cells), cytokines (interleukin‐1β [IL‐1β] and tumor necrosis factor α [TNFα]), interleukin‐1 receptor antagonist (IL‐1Ra), and monoclonal antibodies against IL‐1β and CD44. Results RASF destroyed the bovine cartilaginous matrix within 2 weeks (days 5–12) and the human cartilaginous matrix within 3 weeks (days 10–18). Compared with the effect of RASF alone (mean ± SD 948 ± 180 counts per minute/week), the addition of U937 cells (a monocytic cell line), IL‐1β, or TNFα to the incubation medium increased the destruction of human cartilaginous matrix by at least 71% up to 90% (ranging from 1,618 ± 204 cpm/week to 1,802 ± 307 cpm/week). IL‐1Ra and anti–IL‐1β monoclonal antibodies reduced the destruction of human matrix by 45% and 35%, respectively; this was partially reversed by the addition of U937 cells. The pretreatment of RASF with anti‐CD44 monoclonal antibody (an adhesion molecule and receptor for hyaluronic acid) inhibited the destruction of the cartilaginous matrix by an average of 41% over 3 weeks. Conclusion This model is envisioned to study distinct aspects of human destructive joint diseases under in vitro conditions and to replace and/or supplement animal experiments in basic research and drug testing. Based on the fact that proinflammatory cytokines enhance destruction whereas IL‐1Ra and antibodies against IL‐1β and CD44 inhibit the process, it is concluded that anti–IL‐1– and anti‐CD44–directed therapies may help prevent cartilage destruction in RA.