Concentration and size distribution of IGF-I in human normal and osteoarthritic synovial fluid and cartilage

Abstract

The role of free insulin-like growth factor (IGF-I) in stimulating proteoglycan (PG) synthesis in cartilage has been well documented (e.g., McQuillan et al., 1986). Equally well documented is the enhancing effect of serum addition to the incubation medium. However, it is by no means clear what, if any, is the connection between the latter two: thus in scrum IGF-I is not present in free form but exists in the form of complexes, mainly as a “large complex” of MWt around 140 kD and to a lesser extent as a “small complex” of MWt around 50 kD. Molecules of this size are largely excluded from the matrix of normal human articular cartilage. Moreover, it should be remembered that cartilage in vivo is not in contact with blood, but with synovial fluid (SF). Information about IGF-I in SF is scarce: there is only one set of data available (Schalkwijk et al. 1989) and these only for total IGF-I content.