Synergistic Effect of Substance P with Insulin and Insulin-Like Growth Factor-I on Epithelial Migration of the Transformed Human Corneal Epithelial Cells (SV-40)

On the cornea, daily epithelial resurfacing is a critical process to prevent the loss of normal function, ocular morbidity, corneal structure, and vision loss. There are several components to wound healing, including cellular attachment, migration, and growth. To develop a treatment for corneal epithelial healing, we studied the effect of substance P (SP) on corneal epithelial cell migration using a cell culture system of either transformed human corneal epithelial cells (SV-40), or rabbit corneal epithelial cells (SIRC). We investigated the effect of SP with insulin and insulin-like growth factor-I (IGF-1). We found that SP is synergistic with insulin and IGF-1 on the stimulation of transformed human corneal epithelial migration in a cell culture system, as well as in rabbit SIRC cells. The addition of either SP, insulin, or IGF-1 alone did not greatly affect epithelial migration, while the combination of SP and insulin or SP and IGF-1 markedly stimulated epithelial migration in a dose-dependent manner. The synergistic effects of SP with insulin and SP with IGF-1 were inhibited by the addition of the SP-specific inhibitor (CP96345). However, the effect of insulin and IGF-1 alone were not inhibited by the NK-1-specific inhibitor (CP96345). Our results are consistent with the need for the involvement of the neuropeptide SP in corneal epithelial wound healing of diabetic corneas where nerve-ending dropout occurs. Additionally, almost identical results were obtained with human and rabbit corneal epithelial cells. These results suggest that the maintenance of the normal integrity of the corneal epithelium might be regulated by both humoral and neural factors.