Adipose tissue is an endocrine tissue releasing adipokines suggested to be involved in the pathogenesis of osteoarthritis (OA). Nevertheless, their relative contribution and exact mechanisms are still ambiguous. The aim of this study is to compare serum adipokine levels between end-stage knee OA patients and controls and to relate these serum levels to local parameters of cartilage damage and synovial inflammation.
Serum was collected from 172 severe knee OA patients, shortly before total knee replacement (TKR) surgery and from 132 controls without radiographic knee OA [Kellgren & Lawrence (K&L) = 0]. Serum adiponectin, leptin, and resistin levels were measured by enzyme-linked immunosorbent assay (ELISA). Cartilage and synovial tissue were collected at TKR surgery and assessed for cartilage degeneration and synovial inflammation by histochemistry and biochemical analyses.
The adipokine levels were all distinctly higher in OA patients as compared to controls. Especially adiponectin and leptin were associated with female gender (stand beta = 0.239 and 0.467, respectively, P < 0.001) and body mass index (BMI) (stand beta = -0.189 and 0.396, respectively, P < 0.001). No associations between serum levels of adipokines and cartilage damage (histochemistry, proteoglycan content) were found whereas weak but positive associations with synovial inflammation were found [adiponectin and interleukin-1β (IL-1β), stand beta = 0.172, P = 0.02; resistin and histology, stand beta = 0.183, P = 0.034, adjusted for demographics].
This study suggests an important involvement of adipokines in OA patients considering their high serum levels compared to controls. Associations of systemic adipokines with local synovial tissue inflammation were found, although not represented by similar relations with cartilage damage, suggesting that adipokines are of relevance in the inflammatory component of OA.