Leptin consumption in the inflamed joints of patients with rheumatoid arthritis

Background: Leptin has been shown to participate in bone remodelling and leptin substitution reported to have a protective effect in experimental septic arthritis. Objective: To assess leptin levels in inflamed joints and plasma of patients with RA. Material and methods: Leptin concentrations were assessed in matched blood and synovial fluid samples from 76 patients with RA. Blood samples from 34 healthy subjects acted as additional controls. Results were analysed and correlated with duration and activity of RA, x ray changes, and treatment at time of sampling. Results: In patients with RA, leptin levels were significantly higher in plasma than in synovial fluid samples obtained simultaneously and higher than in control samples. Plasma and synovial fluid leptin levels correlated strongly. Locally in the joint, leptin levels were related to WBC count. Such a relation was not seen in the bloodstream. Leptin levels were not related to sex, age, or disease duration. Difference between leptin levels in plasma and synovial fluid was greater in non-erosive arthritis (5.1 (SEM 1.2) v 3.7 (0.9) ng/ml, p = 0.006), than in patients with erosive joint disease (6.2 (1.0) v 5.4 (0.8) ng/ml, NS). Methotrexate treatment was associated with relatively high plasma leptin levels, while treatment with other DMARDs was associated with lower leptin levels than in patients receiving no DMARD treatment (p = 0.0005). Conclusions: Leptin production was significantly increased in patients with RA compared with healthy controls. Synovial fluid leptin levels were significantly lower than in matched plasma samples, suggesting an in situ consumption of this molecule.