Relationship of plasma and synovial fluid BMP-7 with disease severity in knee osteoarthritis patients: a pilot study

The objective of this study was to investigate bone morphogenetic protein-7 (BMP-7) levels in both plasma and synovial fluid of patients with primary knee osteoarthritis (OA) and to determine their relationship to disease severity. Thirty-two patients with knee OA and 15 healthy subjects were enrolled in the study. Anteroposterior knee radiographs were taken to determine the disease severity of the affected knee. The radiographic grading of OA in the knee was performed using the Kellgren-Lawrence criteria. BMP-7 levels in the plasma and synovial fluid were measured using enzyme-linked immunosorbent assay. The mean plasma BMP-7 concentration of the knee OA patients was significantly higher compared with that of healthy controls (12.1 +/- 1.6 vs 3.5 +/- 0.9 pg/ml, P = 0.001). Although BMP-7 levels in plasma were higher with respect to paired synovial fluid samples, the difference was not statistically significant (12.1 +/- 1.6 vs 10.5 +/- 2.2 pg/ml, P = 0.3). Subsequent analysis showed that plasma BMP-7 levels significantly correlated with disease severity (r = 0.77, P < 0.001). Furthermore, the synovial fluid levels of BMP-7 also correlated with disease severity (r = 0.60, P < 0.001). In addition, plasma BMP-7 levels showed a positive correlation with synovial fluid BMP-7 levels (r = 0.71, P < 0.001). Overexpression of BMP-7 in plasma and synovial fluid is related to progressive joint damage in knee OA. These findings suggest that BMP-7 might serve as a biochemical parameter for determining disease severity in primary knee OA and could play a potential role in cartilage protection and repair of OA.