Serum cysteine proteases and their inhibitors in rheumatoid arthritis: relation to disease activity and radiographic progression

This study aims to investigate the serum levels of cysteine proteases cathepsins B and H and their inhibitors stefin A, stefin B, and cystatin C, as well as traditional inflammatory markers such as C-reactive protein in patients with rheumatoid arthritis and to correlate these markers with scores of disease activity and radiographic progression. Seventy-two patients with rheumatoid arthritis were included from two previously described cohorts of patients with chronic polyarthritis. At inclusion, disease activity was assessed by a 28-joint count, patient global assessment, and serum C-reactive protein. Erosive status of hands and wrists was expressed by the Larsen score and recorded at inclusion and after 1 year. Serum levels of cathepsin B, cathepsin H, stefin A, stefin B, and cystatin C were determined by enzyme-linked immunosorbent assay. Neither cathepsin B nor cathepsin H serum levels were associated with disease activity, presence or progression of erosive disease. Number of swollen joints correlated with serum levels of stefin A and B and correlated negatively with cystatin C serum levels. Erosive disease was associated with high serum levels of C-reactive protein and stefin A and low serum levels of cystatin C. Progression of radiographic destruction was associated with high serum levels of C-reactive protein, stefin A and B, whereas serum levels of cystatin C were not associated with radiographic progression. The findings in this study support further investigation in the regulation of the activity of cathepsins and their inhibitors in erosive rheumatoid arthritis.