Activation and Inhibition of Endogenous Matrix Metalloproteinases in Articular Cartilage: Effects on Composition and Biophysical Properties

Bovine cartilage explants were cultured with 1 mM4-aminophenylmercuric acetate (APMA) to activate endogenous matrix metalloproteinases (MMPs) and changes in biochemical, biomechanical, and physi- cochemical properties were assessed. Additionally, graded levels of either rhTIMP-1 (recombinant human tissue inhibitor of metalloproteinases-1) or L-696-418 (a synthetic metalloproteinase inhibitor) were used to inhibit degradation induced by APMA. Treatment with APMA resulted in as much as 80% loss in tissue GAG content, a greater than threefold increase in denatured type II collagen as determined by the presence of CB11B epitope, and complete loss of biosynthetic activity after 3 days in culture. Physicochemical studies revealed that APMA treatment resulted in a significant increase in tissue swelling response, consistent with damage to the collagen network. Activation of MMPs by APMA also resulted in >80% decrease in equilibrium modulus, dynamic stiffness, and streaming potential and >50% decrease in electrokinetic coupling coefficient. The addition of 4 μM, 400 nM, and 40 nMTIMP inhibited PG loss by 95, 50, and 20%, respectively, and all doses effectively inhibited swelling response. The addition of 4 μMand 400 nML-696-418 inhibited PG loss by 95% while 40 nML-696-418 inhibited PG loss by 60%, and all doses effectively inhibited swelling response. The inhibition of APMA-induced GAG loss by 4 μMTIMP was accompanied by maintenance of streaming potential, electrokinetic coupling coefficient, dynamic stiffness, and equilibrium modulus.