Synovial fluid levels of adipokines in osteoarthritis: Association with local factors of inflammation and cartilage maintenance.

The role of body weight in the pathogenesis of osteoarthritis (OA) - previously considered the sole factor in the association between obesity and OA - is being re-evaluated as the contribution of adiposity to the cartilage degenerative process becomes clearer. The current study has been undertaken to better understand the role of adipose-derived proteins, namely adipokines, in OA. For this purpose, we investigated in patients with OA the relationships between the joint levels of leptin, adiponectin and resistin and those of factors involved in inflammation and cartilage maintenance. The sandwich enzyme-linked immunosorbent assays were used to determine in the synovial fluid (SF) from 35 OA patients, the concentrations of adipokines, interleukin-6 (IL-6) and transforming growth factor-β (TGF-β). The soluble form of leptin receptor (sOb-R) was also examined to evaluate the biological active free form of leptin. Correlation analysis indicate that IL-6 levels are positively related to the levels of resistin and adiponectin. Surprisingly, the free form of leptin, but not the total leptin, is negatively associated with IL-6. Beside, adiponectin is the single adipokine that is correlated with TGF-β. Interestingly, a sexual dimorphism is observed in the study as correlations between adipokines and IL-6 or TGF-β are found only with female OA patients. Taken together, these findings suggest that only adiponectin may contribute to the metabolic changes associated with OA. The three adipokines may also be involved in inflammation, but with opposite effects. Both resistin and adiponectin may exhibit pro-inflammatory activity while the free form of leptin may down-regulate the inflammation.