Clearance of IGFs and insulin from wounds: effect of IGF-binding protein interactions

We have examined the role binding proteins have in regulating the clearance of exogenous growth factors from wounds. Hunt-Schilling chambers were subcutaneously implanted in rats, and the clearance of insulin-like growth factor (IGF) I from the chamber wound fluid was compared with IGF-II, LR3-IGF-I, which binds poorly to IGF-binding proteins (IGFBP), or insulin. Elimination rate constants of the slow phase of the decay curves did not differ between IGF-I and IGF-II. However, LR3-IGF-I and insulin were cleared more rapidly from wound fluid than IGF-I so that the half-lives for IGF-I, IGF-II, LR3-IGF-I, and insulin were 872, 861, 563, and 324 min, respectively. In wound fluid, minimal degradation of the IGFs occurred, whereas insulin was degraded considerably. The increased clearance of LR3-IGF-I and insulin equated with a reduced association with wound fluid IGFBPs, and increased amounts of radioactivity of these peptides were detected in the circulation and urine. These results show that this model of wound repair may be of use in examining the kinetics of growth factors and other bioactive molecules in extravascular spaces and support the hypothesis that IGFBPs can be significant regulators of IGF bioavailability in vivo.