Correlation of plasma and synovial fluid adiponectin with knee osteoarthritis severity

Background and aims: Osteoarthritis (OA) is a chronic degenerative joint disorder of the synovial joint characterized by loss of articular cartilage, osteophyte formation, and alterations of subchondral bone. The purposes of this study were to measure adiponectin concentrations in plasma and synovial fluid of patients with knee OA and to analyze the correlation of adiponectin levels with disease severity.

Methods: Seventy six OA patients (mean age 69.8 ± 1.1 years) and 24 healthy controls (mean age 71.2 ± 1.5 years) were enrolled in this study. OA grading was performed using the Kellgren-Lawrence (KL) criteria by evaluating x-ray changes observed in anteroposterior knee radiography. Adiponectin levels in plasma and synovial fluid were determined by commercial enzyme-linked immunosorbent assay.

Results: Plasma levels of adiponectin were higher in OA patients compared to healthy individuals, but the difference did not reach statistical significance (2428.0 ± 245.1 vs. 2030.3 ± 399.4 ng/mL, p = 0.4). Adiponectin levels in plasma were remarkably higher with regard to paired synovial fluid (2428.0 ± 245.1 vs. 301.3 ± 44.9 ng/mL, p <0.001). Additionally, adiponectin concentrations in plasma and synovial fluid showed significant inverse correlation with disease severity evaluated by KL grading criteria (r = -0.68, p <0.001 and r = -0.47, p <0.001, respectively). Further analysis showed that plasma adiponectin levels positively correlated with synovial fluid adiponectin levels (r = 0.71, p <0.001).

Conclusions: Adiponectin levels in both plasma and synovial fluid decreased significantly as the severity of OA increased. These findings suggested that adiponectin may play a protective role in OA. More studies are warranted to gain insight into the potential utility of adiponectin as a biochemical determinant of disease progression and prognosis.