Calprotectin (S100A8/A9) and S100A12 in inflammatory arthritis : clinical and epidemiological studies of rheumatoid and psoriatic arthritis

Rheumatoid- and psoriatic arthritis (RA and PsA) are the two most prevalent inflammatory joint diseases in Caucasian. Different biomarkers in peripheral blood may contribute in the diagnostic and prognostic process, as well as in assessing the disease activity of the individual patient. The concentration of the leukocyte protein complex calprotectin (S100A8/A9) is increased in inflamed joints and in peripheral blood of patients with various inflammatory diseases. S100A12 is another S100 protein that more recently has been described as a proinflammatory protein in arthritis. Disease manifestations and prognosis in RA and PsA have both articular and non-articular aspects, and these should be adressed during treatment of the patients. The risk of cardiovascular disease is increased in RA, and to a lesser extent in PsA. Supplementation with fish oil has modest beneficial effects in RA both for arthritis and collateral health. The overall aim of the study was to investigate calprotectin and S100A12 as biomarkers of disease activity or distinct clinical features in patients with either RA or PsA. In addition, we wanted to estimate the prevalence of PsA in our population and to explore effects of short-term oral supplementation with seal oil. We found a prevalence of PsA in the county of Hordaland equivalent to 1.95 per 1000. If given a prevalence of psoriasis at 1.4%, this corresponds to a PsA prevalence among psoriatics of 14%. The levels of calprotectin were elevated in stool samples from patients with PsA, suggesting asymptomatic psoriatic enteropathy. In a clinical trial with seal oil to patients with PsA we found improvement in subjective measures and a significant shift in the fatty acid composition in peripheral blood, toward a putative antiinflammatory profile. We found that both calprotectin and S100A12 levels in serum correlate with disease activity parameters in RA. High levels of S100A12 were detected in patients with RA, as well as new conformational states of this protein. The S100 proteins did not perform better than CRP as inflammatory