INHIBITORS OF COLLAGENASE BUT NOT OF GELATINASE REDUCE CARTILAGE EXPLANT PROTEOGLYCAN BREAKDOWN DESPITE ONLY LOW-LEVELS OF MATRIX METALLOPROTEINASE ACTIVITY

Aims-To investigate the level of matrix metalloproteinase activity dur ing the time-course of cartilage explant proteoglycan breakdown; to de termine the effects of selective small-molecule inhibitors of matrix m etalloproteinases on proteoglycan degradation. Methods-The levels of m atrix metalloproteinase activity in cartilage explant cultures and con ditioned media were monitored by use of a quenched fluorescent substra te. The constants for inhibition of certain matrix metalloproteinases by a series of synthetic inhibitors were determined. Bovine and human cartilage explant cultures were treated with interleukin-1, tumour nec rosis factor or retinoic acid and the amount of proteoglycan released into the culture medium in the absence and presence of the inhibitors was quantified. Control experiments, examining the inhibition of other proteinases, and investigating possible toxic or non-specific effects of the inhibitors, were carried out. Results-The profile of inhibitio n of proteoglycan release suggested the involvement of interstitial co llagenase-like, rather than gelatinase- or possibly stromelysin-like, proteinases. No evidence was found for toxic or non-specific mechanism s of inhibition. Very low levels of activity of the known matrix metal loproteinases were present during the time-course of aggrecan breakdow n. Conclusions-A novel collagenase-like proteinase(s) may be involved in cartilage proteoglycan breakdown. Gelatinase-type matrix metallopro teinases do not seem to be involved in this process. Specific collagen ase inhibitors may be therapeutically efficacious in the treatment of arthritis.