Increased levels of serum myeloperoxidase in patients with active rheumatoid arthritis

AimsThe clinical significance of myeloperoxidase (MPO) has been the focus of investigation because it may contribute to the chronic, non-microbial inflammatory process in various diseases. Here, we determined serum MPO levels in rheumatoid arthritis (RA) and other autoimmune or inflammatory conditions, and investigated the associations between MPO levels and disease activity indicators in RA.Main methodsThe distribution of MPO was determined in serum samples from patients with RA, systemic lupus erythematosus (SLE), primary Sjögren's syndrome (pSS), dermatomyositis (DM), or ankylosing spondylitis (AS) and from healthy controls using commercial ELISA kits. Associations of serum MPO levels with the disease variables of RA patients were evaluated.Key findingsAll patient samples analyzed showed higher serum levels of MPO than healthy controls. Furthermore, MPO levels in RA were significantly higher than those in the other diseases with the exception of DM. Higher MPO levels were observed in RA patients with increased C-reactive protein (p = 0.005) or neutrophil percentage (p < 0.001), as well as in those with highly active disease (p < 0.001). Moderate positive correlations between MPO levels and IgM (r = 0.334, p = 0.001), C-reactive protein (r = 0.293, p = 0.003), erythrocyte sedimentation rate (r = 0.240, p = 0.016), or DAS28 (r = 0.350, p < 0.001) were also demonstrated.SignificanceThe MPO concentration is likely to increase in patients with chronic inflammation. The associations between MPO and the disease variables of RA patients support a role for MPO in the inflammatory process of the disease.