Purpose: Insulin-like growth factors (IGFs) and either substance P (SP) or an SP-derived peptide (FGLM-amide) synergistically facilitate corneal epithelial wound healing in vitro and in vivo. The mechanism of this synergism and the clinical potential of these agents were further investigated by determination of the relevant functional domain of IGFs.
Methods: The effects of IGF-derived peptides on corneal epithelial cell migration were evaluated with the rabbit cornea in an organ culture system. Corneal epithelial wound closure in vivo was also evaluated in rabbits after epithelial debridement with n-heptanol.
Results: In the presence of FGLM-amide, peptides corresponding to the C domain of IGF-1 or -2 significantly promoted corneal epithelial migration in vitro to an extent similar to that apparent with the full-length molecules. In contrast, peptides corresponding to the D domain of these growth factors had no such effect. Mutation of serine-34 in the C domain of IGF-1 to alanine abolished the synergistic effect with FGLM-amide on corneal epithelial migration. The C peptide of proinsulin did not affect corneal epithelial migration in the absence or presence of FGLM-amide. The administration of eye drops containing both the C-domain peptide of IGF-1 and FGLM-amide significantly promoted corneal epithelial wound closure in vivo.
Conclusions: The C domain of IGF-1 or -2, for which no biological function has previously been identified, is essential for the synergistic effect of these growth factors with SP on corneal epithelial migration.