Objective: To test the activity of elastase, collagenase and glutathione reductase in the synovial fluid (SF) of patients with rheumatoid arthritis (RA) and in patients with osteoarthritis (OA); to correlate the elastase and collagenase activity with the glutathione reductase activity, which is important for the inactivation of oxygen free radicals.
Methods: 24 patients affected by osteoarthrosis and 24 patients affected by rheumatoid arthritis took part in the study. We measured elastase activity towards the substrate metoxysuccinyl-alanyl-alanyl-prolyl-valyl-p-nitroanilide (MeOSuc-ala-ala-proval-p-NA) which is highly specific for elastase, and insensitive to the other serine proteases, such as cathepsin G; collagenase activity was measured using [14C]-acetylated collagen as the substrate. Glutathione reductase activity was measured following the oxidation of nicotinamide adenine dinucleotide phosphate reduced (NADPH) in the presence of oxidized glutathione (GSSG).
Results: The concentrations of elastase, collagenase and glutathione reductase were statistically higher in patients with RA than in patients with OA. Moreover, in the SF of patients with RA we found positive correlation between enzyme activity levels.
Conclusion: These results confirm a high activity of collagenase and elastase in the SF of patients with RA, which is about 30 times higher than that found in the SF of patients with OA. These data underline the synergic action of these enzymes in the pathogenesis of joint damage. RA patients also exhibit higher levels of glutathione reductase, which is important for the detoxification pathway of oxygen free radicals. However, compared with findings for collagenase and elastase, the increase in glutathione reductase is only three times higher than level found in the SF of OA patients. The limited increase in glutathione reductase activity during the inflammatory process might lead to an insufficient protective effect at the joint level in rheumatoid arthritis.