IDENTIFICATION AND CHARACTERIZATION OF INSULIN-LIKE GROWTH-FACTORS (IGFS), IGF-BINDING PROTEINS (IGFBPS), AND IGFBP PROTEASES IN HUMAN SYNOVIAL-FLUID

The insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBP s) in human synovial fluid play an important role in maintaining artic ular cartilage metabolism. In this study we measured the concentration s of IGF-I, IGF-II, and IGFBP-3 in normal human synovial fluid by RIA, and characterized the IGFBPs by Western ligand blot (WLB), Western im munoblot, and immunoprecipitation. We also extended the study and comp ared normal synovial fluid to synovial fluids from patients with osteo arthritis (OA) and rheumatoid arthritis (RA). The concentrations of IG F-I, IGF-II, and IGFBP-3 in normal synovial fluid were 19 +/- 3 (mean +/- se), 194 +/- 14, and 349 +/- 65 ng/mL, respectively. In synovial f luid of patients with OA, IGF-I levels were elevated, whereas IGF-II w as decreased, and the IGFBP-3 level was similar to the control value. In patients with RA, both IGF-I and IGFBP-3 were elevated, whereas IGF -II remained unchanged. WLB and immunoprecipitation of normal synovial fluid revealed IGFBP-1 (26-29 kDa), IGFBP-2 (32 kDa), IGFBP-3 (42- to 39-kDa doublet), and IGFBP-4 (24 kDa); the IGFBP-3 doublet was very f aint. In RA synovial fluid, all IGFBPs were dramatically increased, wh ereas little change was seen in the synovial fluid of OA. Western immu noblot against IGFBP-3 revealed a prominent 50-kDa immunoreactive frag ment of IGFBP-3 in synovial fluids of normal adults as well as in thos e of RA and OA patients. This was concurrent with detectable IGFBP-3 p rotease activity, which was characterized to be of the metallo- and se rine protease family. Thus, in normal synovial fluid, there is a balan ce of circulating IGF, IGFBP, and proteases to modulate the bioactivit y of IGF. In pathological states, the increased IGF-I concentrations w ere accompanied by an increase in IGFBP-3 levels in synovial fluid. Th ese findings suggest that alteration of the IGF and IGFBP axis in path ological states may be important for understanding the underlying path ophysiology of disordered articular growth and metabolism.