P85 INTERLEUKIN-1 ALPHA IN COMPARISON TO INTERLEUKIN-1 BETA IS A MORE POTENT STIMULATOR OF AGGRECANASE MEDIATED AGGRECAN DEGRADATION IN HUMAN ARTICULAR CARTILAGE

Abstract

Purpose: Aggrecan is the predominant proteoglycan in the extracellular matrix of articular cartilage. One of the early steps in initiation of cartilage degradation is loss of proteoglycans, which leads to further degradation of the collagen network. Interleukin1 (IL-1) is a potent pro-inflammatory cytokine associated with the pathology of osteoarthritis (OA). However, controversy exists regarding the potency of IL-1alpha (IL-1α) compared to IL-1beta (IL-1β) on degradation of articular cartilage. Therefore, the aim of the present work was to assess the potential of IL-1α and IL-1β on human articular cartilage degradation, through quantifying MMP and aggrecanase activity with special emphasis on protease generated fragments of aggrecan. Methods: Articular cartilage was obtained from OA patients undergoing total kne arthroplasty. Articular cartilage explants were cultured for 21 days with refreshment of medium every 3rd day in the presence of 100 ng/mL IL-1α or 100 ng/mL IL-1β to stimulate cartilage degradation. As negative control, explants were cultured without stimulation. Cartilage degradation was monitored by measuring the conditioned medium in 2 independent sandwich assays (1) 342-G2 assay, composed of the capturing antibody AF-28 against the 342FFGVG neo-epitope generated by MMP-cleavage and the monoclonal antibody F-78 binding to both the Globular 1 (G1) and Globular 2 (G2) domain of aggrecan; (2) 374-G2 assay, made up by the capturing antibody BC-3 against the 374ARGSVI neo-epitope created by aggrecanase cleavage and F-78. Results: Both IL-1α or IL-1β stimulated aggrecanase mediated cartilage degradation as measured by the 374-G2 assay. However, IL-1α was approximately 200% more potent in inducing aggrecanase activity in human chondrocytes compared to IL-1β at equimolar concentrations. Neither IL-1α or IL-1β treatment of the human articular cartilage explants resulted in increased release of MMP generated fragments of aggrecan quantified by the 342-G2 assay. Conclusions: Both IL-1α or IL-1β induce aggrecanases in human osteoarthritic cartilage. However, IL-1α seems to be approximately 200% more potent than IL-1β, suggesting important differences in cartilage metabolism induced by these two cytokines.