Myeloperoxidase (MPO) in Synovial Tissue and Serum in Patients with Psoriatic Arthritis and Osteoarthritis—A Pilot Study

The aim of this study was to determine the serum level of myeloperoxidase (MPO) and level of synovial fluid MPO of patients with psoriatic arthritis (PsA); the presence of myeloperoxidase positive cells (MPO+) in the synovial tissue of the same patient and correlations between this results with disease activity. Methods: Serum samples and synovial tissue samples were collected from 36 patients with PsA and 42 patients with gonarthrosis (GoA). The serum level and synovial fluid level of MPO of the PsA patients was assessed by ELISA. Immunohistochemical methods were used to detect MPO+ cell expression in the tissue samples. The results of MPO+ cells in the synovial tissue were analyzed by experienced histologists and were evaluated according to the intensity of staining. Routine disease activity indices - VAS, DAPSA, PASDAI, mСPDAI were used to assess PsA activity. Statistical analysis was performed using SPSS version 26.0 (SPSS Inc., Chicago, Illinois, USA). Results: The serum level of MPO in patients with PsA was 471.56±41.7 ng/ml, the serum level of MPO in patients with GoA was 221.98±22.1 ng/ml, the difference between the groups was significant (p=0.05). The level of MPO in the synovial fluid of patients with PsA was 309.56±23.6 ng/ml, and in patients with GoA - 103.4±21.5 ng/ml, the difference between the groups was significant (p=0.05). The expression of MPO+ cells in the synovial tissue of patients with PsA was significantly higher than that in patients with GoA (p=0.01). The disease activity indices - VAS, DAPSA, PASDAI, mCPDAI showed a significant positive relationship with the expression of MPO+ cells in the synovial tissue and serum MPO in patients with PsA (P = 0.05). Conclusions: MPO plays an important role in patients with psoriatic artritis. The level of MPO in serum and synovial fluid reflects disease activity. MPO+ cells in the synovial tissue of patients with PsA may be a useful biomarker to arthritis activity .This suggests the need to investigate therapeutic approaches aimed at blocking MPO+ cells with appropriate biological therapeutic molecules, which will reduce potential joint damage. Keywords: MPO, synovial tissue, psoriatic arthritis The results are related to project No. NO-07/2025 of the Medical University of Plovdiv, Bulgaria Highlights • Myeloperoxidase (MPO) is an enzyme involved in inflammatory joint diseases such as psoriatic arthritis (PsA) • Serum MPO levels correlate with disease activity indices in patients with PsA • There is a significant presence of MPO+ positive cells in the synovial membrane of patients with PsA • MPO levels can be used as a biomarker for disease activity in serum and synovial fluid studies in patients with PsA • There is a need to develop MPO inhibitors that could be used as new therapeutic strategies in the treatment of psoriatic disease