Cathepsin B and cysteine protease inhibitors in human osteoarthritis

Abstract

The aim of this study was to determine the involvement of cathepsin B and its inhibitors in the proteolytic degradation of human osteoarthritic (OA) tissue. The characteristics of the cathepsin B found in both normal and OA cartilage and synovium were similar to those of the lysosomal cathepsin B. Two inhibitors of cysteine proteases were found with a molecular weight of 67,000 and 16,000 Da. The cartilage cathepsin B level of OA specimens (54.8 ± 7.3 units/μg of DNA) was greater than the controls (39.8 ± 3.2 units/μg of DNA). Mild-moderate graded samples (78.1 ± 12.0 units/μg of DNA) had significantly higher levels of enzyme activity than the severely graded ones (31.4 ± 3.9 units/μg of DNA, p < 0.001) and controls (p < 0.01). Compared to controls (2.3 ± 0.4 units/mg of tissue w.w.), cysteine protease inhibitory activity in OA cartilage was decreased in specimens with severe lesions (1.5 ± 0.2 units/mg of tissue). This was particularly noted in patients who had not received steroid injections (1.2 ± 0.3 units/mg of tissue, p < 0.05). In OA synovia, the cathepsin B level was greater (40.7 ± 7.4 units/mg of tissue w.w., p < 0.02) than in the controls (13.6 ± 3.7 units/mg of tissue). The cysteine protease inhibitory activity was similar in OA synovium (1.7 ± 0.2 units/mg of tissue w.w.) and in controls (1.5 ± 0.3 units/mg of tissue). This data demonstrated an imbalance between the levels of cathepsin B and cysteine protease inhibitors in OA tissue. A decrease of specific inhibitors could be an important contributing factor, particularly in more severe lesions.