Effects of plasminogen and interleukin-1 beta on bone resorption in vitro

Inflammatory bone resorption, a characteristic feature of periodontal disease and rheumatoid arthritis, appears to be mediated by interleukin-1 beta (IL-1 beta). IL-1 beta has been shown to stimulate a wide range of proteolytic enzymes, including collagenases and plasminogen activators, in particular chondrocytes, synovial cells, and isolated osteoblasts. In this study, we have examined the hypothesis that IL-1 beta may stimulate bone loss by inducing the activity of plasminogen activators (PAs) in bone cultures. The latter would convert plasminogen to plasmin, which in turn can activate precursor procollagenase to collagenase. Active collagenase would then break down the bone collagen matrix. In the present study, release of 45Ca from fetal rat long bones in culture was studied in the presence of plasminogen and IL-1 beta. Plasminogen and IL-1 beta separately enhance resorption of fetal rat long bones in vitro. When plasminogen and IL-1 beta are added together at suboptimal levels, mainly additive effects are observed. The presence of heat-inactivated serum does not alter these results. These data tend to indicate that IL-1 beta is stimulating bone resorption through both PA-dependent and PA-independent pathways.