Levels of metalloproteases and tissue inhibitor of metalloproteases in human osteoarthritic cartilage.

Human articular cartilage contains 2 distinct metalloproteases which degrade proteoglycan. One protease acts optimally at pH 5.3 and the other at pH 7.2. In addition, cartilage contains a tissue inhibitor of metalloproteases (TIMP) that inhibits both proteases. Methods have been developed for the estimation of metalloproteases and TIMP in extracts of cartilage prepared in buffered 2 M guanidine-HCl. In osteoarthritic cartilage, levels of the 2 metalloproteases increase 3-fold or more, while the level of TIMP remains constant. It is postulated that a balance is maintained between inhibitor and metalloprotease levels in normal cartilage and that in osteoarthritis increased secretion of proteases upsets this balance and results in degradation of the extracellular matrix.