Role of interleukin‐1, tumor necrosis factor α, and interleukin‐6 in cartilage proteoglycan metabolism and destruction effect of in situ blocking in murine antigen‐ and zymosan‐induced arthritis

Abstract

Objective. To determine the involvement of interleukin‐1 (IL‐1), tumor necrosis factor (TNF), and IL‐6 in the cartilage pathology of murine antigen‐induced arthritis (AIA) and zymosan‐induced arthritis (ZIA). Methods. Arthritis was induced by intraarticular injection of zymosan in naive mice or by subcutaneous injection of methylated bovine serum albumin in sensitized animals. Mini‐osmotic pumps releasing human recombinant IL‐1 receptor antagonist (IL‐1ra) protein were implanted intraperitoneally 2 days before arthritis induction, and neutralizing antibodies directed against murine IL‐1α, IL‐1β, TNFα, or IL‐6 were administered 1 day before. Proteoglycan (PG) synthesis and degradation were assessed in patellar cartilage. Results. Murine IL‐1α and IL‐1β injected intraarticularly at doses of 0.1–100 ng suppressed chondrocyte PG synthesis. The highest dose of TNF tested (100 ng) decreased PG synthesis marginally. In contrast, the maximum dose of IL‐6 (1 μg) stimulated PG synthesis 2 days after injection. Treatment of AIA with neutralizing monoclonal antibodies against either TNFα or IL‐6 did not reduce either the PG degradation or the suppression of its synthesis. However, treatment with anti‐IL‐1 (α + β) polyclonal antibodies totally prevented PG suppression, although the initial breakdown of PG was unaffected. This effect was confirmed when IL‐1ra was administered in high doses. Moreover, treatment of ZIA with anti‐IL‐1 (α + β), but not with anti‐TNF, resulted in normal PG synthesis, confirming the key role played by IL‐1 in the inhibition of PG synthesis. Treatment of AIA with anti‐IL‐1 did not affect inflammation during the acute phase, but a significant reduction of ongoing inflammation was noted at day 7, and there was a marked reduction in the loss of cartilage PG. Conclusion. The suppression of PG synthesis in both ZIA and AIA in mice is due to the combined local action of IL‐1 (α + β), and neither IL‐6 nor TNF is involved. Moreover, the normalization of PG synthesis brought about by blocking of IL‐1 ameliorates the cartilage damage associated with AIA.