Objective: Rheumatoid arthritis (RA) is a systemic chronic inflammatory joint disease, whereas osteoarthritis (OA) is a local joint disease with low-level inflammatory activity. The pathogenic role of the adipocytokine adiponectin is largely unknown in these diseases. We hypothesized (1) that plasma adiponectin concentrations differ in healthy controls and patients with early disease-modifying antirheumatic drug (DMARD)-naive RA, chronic RA, and OA; (2) that changes in adiponectin are observed during methotrexate (MTX) treatment of chronic RA; and (3) that adiponectin correlates to disease activity measures in RA.
Methods: Plasma adiponectin was analyzed with a validated in-house immunoassay. We measured adiponectin in healthy controls (n = 45) and patients with early DMARD-naive RA (n = 40), chronic RA (n = 74), and OA (n = 35). In a subgroup of patients with chronic RA (n = 31), the longitudinal effect of MTX treatment on adiponectin (Week 0 vs Week 28) was investigated.
Results: Adiponectin differed significantly between healthy controls (mean 4.8 +/- SD 2.7 mg/l) and the 3 groups, with 8.9 +/- 4.8 mg/l in early RA, 11.6 +/- 5.6 mg/l in chronic RA, and 14.1 +/- 6.4 mg/l in OA. Longitudinally, MTX treatment increased adiponectin significantly from 9.7 +/- 4.5 mg/l at Week 0 to 11.0 +/- 4.5 mg/l at Week 28 in chronic RA. No correlations to disease activity measures were found.
Conclusion: Both early DMARD-naive and chronic RA were associated with higher plasma adiponectin compared to healthy controls, but lower plasma adiponectin than OA. Adiponectin increased 13% during MTX treatment. In patients with RA and OA body mass index, age, sex, and disease activity measures failed to explain the findings.