Objective: To explore the relationship between osteopontin (OPN), its downstream product thrombin-cleaved osteopontin (NTOPN) and radiographic changes in osteoarthritis (OA).
Methods: The levels of OPN and NTOPN in serum and synovial fluid were tested by enzyme-linked immuno sorbent assay (ELISA) kit in 22 OA patients and 21 health controls. The correlation between the above parameters and clinical data such as radiology changes of OA patients was analyzed.
Results: The serum level of OPN in the OA group was positively correlated with C reactive protein (CRP) (r = 0.574, P = 0.005). The serum level of OPN in the OA group was slightly lower than that in the healthy control group [(1.8 ± 0.5) µg/L vs (1.7 ± 1.1) µg/L, P > 0.05]. Similarly, the serum level of NTOPN in the OA group was significantly higher than that in control group [(21.1 ± 11.7) µg/L vs (14.7 ± 3.6) µg/L, P < 0.05]. Meanwhile, serum NTOPN level in female patients was significantly higher than that in male patients[(23.2 ± 11.80) µg/L vs (11.1 ± 4.9) µg/L, P < 0.05]. In synovial fluid of OA group, the level of OPN was (7.75 ± 2.33) µg/L,NTOPN was (0.91 ± 0.49) µg/L and the ratio of NTOPN/OPN was 0.12 ± 0.08. The level of OPN of synovial fluid in the OA group was positively correlated with CRP (r = 0.574, P = 0.005).NTOPN-to-OPN ratio of synovial fluid in the OA group was positively correlated with Kellgren-Lawrence grade (r = 0.535, P = 0.022).
Conclusions: The serum level of OPN is correlated with severity of inflammation in the OA patients. Meanwhile, NTOPN-to-OPN ratio of synovial fluid is correlated with OA severity. As a downstream bioactive product of OPN, NTOPN may play an important role in OA pathogenesis.Whether these parameters can be used as predictors of joint lesion severity and inflammatory status is worth further study.