Evidence for metalloproteinase and metalloproteinase inhibitor imbalance in human osteoarthritic cartilage

Abstract

Cartilage specimens from tibial plateaus, obtained from 13 osteoarthritic (OA) patients and seven controls, were selected from three regions: zone A, center of fibrillated area; zone B, area adjacent to fibrillation, and zone C, remote region of plateau. Acid and neutral metalloproteinases and tissue inhibitor of metalloproteinase (TIMP) were extracted with 2 M guanidine. Methods were developed to selectively destroy either proteinases or TIMP to prevent cross-reaction during assay. Acid and neutral proteinases were elevated approximately 150% in OA; TIMP was elevated approximately 50%. A positive correlation (r = 0.50) was found between acid and neutral proteinase activities in OA, but not in controls. Both proteinases were elevated two-to threefold in zones A, B, and C. However, the self-active form of the acid metalloproteinase was elevated only in zones A and B (200%); it correlated well with the Mankin scores, whereas the total activities did not. TIMP was elevated (50%) only in zones A and B. Both the proteinase levels and the Mankin score were elevated to a greater extent in the medial, than in the lateral, compartment. Titration of TIMP against the two metalloproteinases indicates that there is a small excess of inhibitor over enzymes in normal cartilage. In OA, TIMP does not increase to the same extent as the proteinases; the resultant excess of proteinases over TIMP may contribute to cartilage breakdown.