Effects of tetracyclines on the production of matrix metalloproteinases and plasminogen activators as well as of their natural inhibitors, tissue inhibitor of metalloproteinases-1 and plasminogen activator inhibitor-1

OBJECTIVE: Evaluation of tetracycline effects on the expression of MMP-1, MMP-3, tissue inhibitor(s) of metalloproteinase-1 (TIMP-1), plasminogen activators (PA), and PA inhibitor-1, which are all involved in the ultimate regulation of MMP activity could provide new insight into how tetracyclines achieve their cartilage preserving effects. MATERIALS AND METHODS: We used bovine articular chondrocytes cultured in alginate gel beads for our studies which were initially treated with 10 microM tetracyclines in the presence of IL-1. Only significant effects were studied at additional concentrations. Expression of mRNA was analyzed by RT-PCR-ELISA. The activity of enzymes and TIMP was measured by functional assays; whereas, the level of PAI-1 was determined by ELISA. RESULTS: Treating chondrocytes with IL-1 induced the expression of MMPs and downregulated TIMP-1 but stimulated both the expression of PAs and PAI-1. When tested at 10 microM only minocycline reduced collagenase activity and expression of MMP-1. Further pharmacokinetic analysis revealed IC50 values of 26 microM and 16 microM for the inhibition of collagenase activity and mRNA expression, respectively. Production of MMP-3 was only decreased by tetracycline (IC50 = 45.4 microM). No effects of tetracyclines could be observed on proteoglycan degradation, TIMP activity and the production of PAs, PAI-1, and TIMP-1. CONCLUSIONS: We conclude that the inhibition of MMPs by tetracyclines occurs mainly via down-regulation of the respective gene expression.