The association of adipokine levels in plasma and synovial fluid with the severity of knee osteoarthritis

Objective. We sought to determine the association between plasma and SF levels of leptin and adiponectin in patients with knee OA. Methods. Plasma and SF levels of adipokines and soluble leptin receptor (sOB-R) were determined by ELISA in 96 patients with knee OA at different stages, according to Ahlback's classification. Results. Levels of adiponectin, leptin, sOB-R and free leptin in plasma and SF did not differ significantly across categories of OA severity. However, the ratio of SF to plasma leptin was significantly lower in the advanced OA stage compared with early stages of the disease (P = 0.02). After adjustment for sex and BMI, plasma leptin positively correlated with categories of OA severity (r = 0.23, P = 0.02), whereas SF/plasma leptin negatively correlated with OA stage (r = -0.27, P = 0.01). Cluster analysis showed that all men were included in one cluster and distributed in different stages of OA, whereas women formed three clusters with similar BMI, but those who were older and had the highest plasma leptin levels suffered from advanced OA. Conclusion. Plasma leptin positively correlated with the severity of knee OA. The ratio of SF to plasma leptin might be a marker related to the severity of knee OA. Further studies should investigate whether similar associations exist in other joints affected by OA.