Insulin-like growth factor I and its binding proteins 3 and 4 are increased in human inflammatory synovial fluid

Objective. To measure insulin-like growth factor I (IGF-I) and its binding proteins (IGFBP) in human synovial fluid (SF), as IGF-I resistance in the chondrocyte was implicated in the pathogenesis of inflammatory arthritis. Methods. Ten patients with inflammatory arthritis and 7 controls were evaluated. IGF-I and IGFBP-3 were measured by radioimmunoassay while all IGFBP were evaluated by Western ligand blotting. Results. Serum IGF-I did not differ between patients and controls (22.3 ± 2.9 vs 22.0 ± 3.0 nmol/l), while significantly higher values were found in inflammatory SF compared with noninflammatory SF (14.7 ± 1.5 vs 10.2 ± 1.2 nmol/l; p = 0.05). IGFBP-3 and IGFBP-4 were the most prominent bands found in inflammatory SF by Western ligand blotting. The 24 kDa IGFBP-4 band appeared faintly in 2 noninflammatory effusions and was nearly absent in others. IGFBP-3 levels in sera from the 2 groups did not differ (2.9 ± 0.3 vs 2.5 ± 0.3 mg/l), but were significantly higher in inflammatory compared with noninflammatory effusions (1.5 ± 0.2 vs 0.9 ± 0.2 mg/l; p = 0.05). Conlusion. The pattern of IGFBP in SF differs in inflammatory versus noninflammatory joints.