Increased level of C3 in synovial fluid in patients with activated osteoarthritis as a diagnostic and therapeutic target – pilot group of patients from the Rheumatology Department at UMHAT Burgas

The clinical course of osteoarthritis (OA) indicates the role of low-grade synovitis as the main driver of the degenerative process. Components of the extracellular matrix, fibronectin isoforms, and fragments of hyaluronic acid are presumed ligands for DAMPs (particularly TLR). Complement fractions bind to the corresponding receptors on the cell membranes of chondrocytes and synoviocytes through TLR. Does the complement cascade play a role only as a clearing system and/or a leading pathogenetic factor in activated OA? The aim of this study is to answer this question. The study included 50 patients with activated OA of the knee joint. We examined the levels of C3 and C4 complement fractions in the blood plasma and synovial fluid. We found that the values of these proteins in synovial fluid were on average 34.90% for C3 and 30.97% for C4 of their values in blood plasma, with a generally accepted norm of 10% for complement levels in a healthy joint. The observation regarding the strength of correlation between the above results and the radiological stage confirmed a stronger correlation of the obtained results in the earlier stages of the disease when the activity of the repair processes is more pronounced. In this way, we objectified the pathogenetic role of complement in the arthritic process, as well as its role in clearing the joint space from degradation products. The question arises whether pharmacological intervention to balance complement activation could represent a future therapeutic strategy in the treatment of OA and prevent its progression.