Insulin-like growth factor I (IGF-I) and IGF-Binding proteins in rat wound fluid

Insulin-like growth factors (IGFs) play an important role in tissue repair, including healing of dermal and epidermal injury. In this study we have measured changes in the IGF:IGF-binding protein (IGFBP) profile of rat wound fluid (WF) collected after sc implantation of Hunt-Schilling chambers for 21 days. WF IGF-I levels 1 day after implantation were equivalent to plasma levels, then fell during the first 7 days before recovering to approximately two thirds of plasma levels by day 21. Western ligand blots of whole WF revealed a profile qualitatively similar to that found in plasma, although the intensity of the IGFBP-3 band was significantly less than that in plasma. Neutral gel chromatography of pooled day 14 WF, after in vitro incubation with [125I]IGF-I, separated the radioligand into three distinct regions of 150, 40, and 7.5 kDa. However, compared to plasma recovery of[125I]IGF-I in the 150-kDa region in WF was reduced, and that in the 40-kDa region was increased. Ligand blotting of the WF-derived neutral gel fractions revealed IGFBP-3 within the 150-kDa complex. Incubation of WF with plasma (1:1, vol/vol) resulted in a progressive decline in the intensity of the plasma IGFBP-3 band. Protease inhibitors, including EDTA, antipain, or aprotonin, inhibited this process. We have described the changes over time in WF IGF-I concentrations, characterized the IGFBP profile, and demonstrated the presence of IGFBP-3 proteolytic activity in WF. The latter may play a role in the regulation of IGF bioavailability during the repair process.