Plasma osteopontin is correlated with bone resorption markers in rheumatoid arthritis patients

To assess whether any form of osteopontin (OPN) is correlated with bone resorption markers or treatment effects in rheumatoid arthritis (RA).

Subjects comprised 119 patients with RA. RA disease activity was evaluated by Disease Activity Score (DAS) 28, erythrocyte sedimentation rate (ESR), and levels of C-reactive protein (CRP), rheumatoid factor (RF) and matrix metalloproteinase (MMP)-3. OPN levels in plasma and urine were measured by enzyme-linked immunosorbent assay (ELISA). Levels of tartrate-resistant acid phosphatase (TRACP) 5b in serum and C-terminal telopeptide of type 1 collagen (CTX)-1 in urine were measured by ELISA. Patients were divided into responder and nonresponder groups, and OPN levels were compared at baseline and after treatment.

Levels of full-length OPN in plasma (P-fOPN) were significantly correlated with levels of TRACP 5b (r = 0.44, P < 0.001), urine CTX-1 (r = 0.26, P = 0.004) and MMP-3 (r = 0.34, P < 0.001). Levels of TRACP 5b were significantly correlated with age (r = 0.25, P = 0.007), but levels of P-fOPN were not. After treatment, plasma OPN levels were significantly decreased in responders (P = 0.003). Levels of full-length or thrombin-cleaved forms of OPN in urine were not correlated with TRACP 5b or CTX-1.

Our results suggest that plasma OPN may reflect inflammatory bone destruction in RA patients.