Fibroblast growth factor-21 concentration in serum and synovial fluid is associated with radiographic bone loss of knee osteoarthritis

We aimed to evaluate whether FGF-21 concentration in serum and synovial fluid (SF) is associated with radiographic bone loss of knee osteoarthritis (OA). A total of 186 OA patients and 108 controls were recruited. The radiographic bone loss of knee OA was assessed by the Ahlback grading scale. FGF-21 concentration in serum and SF was measured by enzyme-linked immunosorbent assay (ELISA). We demonstrated that OA patients had significantly higher serum FGF-21 concentration compared with controls (204.30 [range 158.25-279.16] ng/L vs. 130.72 [range 94.93-218.03] ng/L, p < 0.01). FGF-21 concentration in serum was well correlated with that in paired SF samples (r = 0.668, p < 0.001). In OA patients, those with a higher Ahlback grade had significantly higher serum and SF FGF-21 concentration (p < 0.001 for both). FGF-21 concentration in serum and SF was significantly and independently associated with the Ahlback grade (r = 0.403, p < 0.001 and r = 0.410, p < 0.001; respectively). These findings indicated that FGF-21 might be a potential biomarker for predicting bone loss of OA. Therapeutic interventions by blocking FGF-21 signaling pathways to delay the degenerative process of OA warrants further investigations.